From Left 4 Dead Wiki, the free Left 4 Dead info source anyone can edit.
Left 4 Dead includes achievements for Steamworks and Xbox LIVE. There are 73 achievements in all for the PC version of Left 4 Dead, but only 65 for the Xbox 360 version; the Outbreak achievement is not in the Xbox 360 version of the game and Survival Pack on Xbox 360 adds no new achievement due to technically being only a patch, not a DLC. There are currently 65 achievements for Left 4 Dead 2.
Survival Pack adds 7 new achievements to Left 4 Dead for the PC version only.
Crash Course adds 10 new achievements to Left 4 Dead.
The Passing adds 10 new achievements to Left 4 Dead 2.
The Sacrifice adds 5 new achievements to both Left 4 Dead and Left 4 Dead 2.
Note: Since the Crash Course update, achievements cannot be earned with cheats turned on (sv_cheats = 1). However, one way is to play on Versus mode with everyone helping each other to get achievements.
Left 4 Dead Hide

Campaign
 	MERCY KILLER	(15G)
Survive the No Mercy campaign.
This can be acquired by surviving the campaign on any difficulty.
"Mercy killing" is another term for euthanasia.

 	CRASH-PROOF	(15G)
Survive the Crash Course Campaign.
This can be acquired by completing the campaign on any difficulty.
Crash-Proof is a play on the term "bulletproof."
It may also be a reference to the film Death Proof.

 	TOLL COLLECTOR	(15G)
Survive the Death Toll Campaign.
This can be acquired by completing the campaign on any difficulty.
A toll collector is someone who collects a toll that must be paid for using a bridge, ferry, or other tolled transportation.
This is also a reference to Charon, who collected a toll from those trying to cross the river Styx in the underworld.

 	DEAD BARON	(15G)
Survive the Dead Air campaign.
This can be acquired by completing the campaign on any difficulty.
This achievement's name is a parody of the Red Baron.

 	GRIM REAPER	(15G)
Survive the Blood Harvest campaign.
This can be acquired by completing the campaign on any difficulty.
The Grim Reaper is the mythological physical embodiment of death, who is often portrayed with a scythe (a traditional farming tool).

Survivor
 	DRAG AND DROP	(20G)
Rescue a Survivor from a Smoker's tongue before they take damage.
This requires you to shoot a Smoker who has grabbed a player. It takes until the Smoker drags the character directly to the Smoker before the Smoker can deal damage.
Just as the Survivor is grabbed by Smoker quickly melee the Survivor or shoot the Smoker
Smokers inflict dragging damage in Versus mode, it is easier to achieve this in the other modes.

 	BRAIN SALAD	(15G)
Make 100 headshot kills.
Aim high when firing into Infected crowds with a shotgun, pick off Infected from a distance if they haven't noticed you yet, and remember that crouching improves accuracy with most guns. Even if you're not trying to get this achievement, you'll probably get it after a while of playing the game normally.
A successful headshot with any weapon will kill a Common Infected on any difficulty, so feel free to use Pistols.
This is easiest to achieve during The Town. Simply use the Hunting Rifle and pick off wandering infected from atop the roof. If you go back into the building, chances are, a few will respawn (or hidden ones will show themselves). Since you're almost literally inside the saferoom, you have unlimited ammo. Just be aware, doing this for too long will provoke a Horde attack.

 	TONGUE TWISTER	(20G)
Kill a Smoker who has grabbed you with his tongue.
You MUST shoot the Smoker as soon as it grabs you. You have roughly a second to kill the Smoker.
If the Smoker grabs you by its tongue, quickly turn and shoot him. Assault Rifle or Hunting Rifle is preferred due to their long range. If you wait long enough you will be constricted and won't be able to kill him.
Use of the 180 flip could help one to quickly face the smoker constricting them from behind.
A tongue-twister is a phrase that is difficult to say.

 	PYROTECHNICIAN	(20G)
Blow up 20 Infected in a single explosion.
Throw a pipe bomb when you see a large horde approaching, such as a panic event. Also throw a Pipe bomb if you enter a large area filled with idle Infected.
You can fulfill this achievement either by throwing a pipe bomb or by blowing up explosives. This achievement should be attempted in finales or Crescendo Event, as at those times there are a lot of Infected in large groups. A perfect instance to do this is the start of Dead Air where there is a Pipe bomb on the table. All you need to do is pick it up and throw it over the wall at the Infected without opening the door.
A pyrotechnician is someone who specializes in the handling of explosives, usually for entertainment purposes.
It is unknown whether a Propane Tank could be used to earn this achievement. However, it would be incredibly difficult to do.

 	BLIND LUCK	(20G)
You or another Survivor take no damage after being vomited on by a Boomer.
While you or another Survivor is covered in bile, throw a Pipe bomb to lure away most of the Infected. This should leave you with a good chance of receiving no damage.
Try to be vomited in a room with a single entry. That way you and your teammates can cover the entrance easier. The preferred weapons are the Auto Shotgun and the Assault Rifle. Try not to hit your teammates during the attack. You can also try throwing a Pipe bomb. Note that the time you count as being "vomited on" is sightly longer than the time your screen is covered in bile, so the safest option is to wait until you get the achievement notification.
If only one or two people have been slimed, they should move to the back of the room/closet. The horde will only attack them, and being at the back will give the team more time to thin the Infected numbers. Aside from that, employ standard turtling tactics (Survivors in the front crouch, shoot, and melee, and Survivors in the back fire over them). If you're slimed and don't know what you're aiming at, melee spam.
Blind luck is a term for a favorable outcome when the affected party had little opportunity to affect the outcome. Here, blind refers to the Survivors' visions being blurred by the vomit.

 	MY BODYGUARD	(15G)
Protect any Survivor from an attacking Infected 50 times.
Whenever you shoot an Infected attacking another person, a message will pop up saying you just protected that person. You must do this 50 times. This is gained by using melee or shooting to get Hunters and Smokers off Survivors, or shooting a Common Infected that is attacking an unaware Survivor in the back.
Watch your teammates' backs excessively when a horde is attacking. You can get this achievement just by playing long enough.
You can still protect your teammates while incapacitated. Simply fire your Pistol(s) from the ground.
Protecting a Survivor from a Special Infected while incapacitated will also earn you the achievement 'Ground Cover' in the process.

 	TANKBUSTERS	(20G)
Kill a Tank without it dealing any damage to a Survivor.
ALWAYS keep your distance from the Tank. As long as your health is high enough, you can easily outrun him, but don't let him get too close.
Set the Tank on fire at your own peril. Fire will kill him within 30 seconds, but it will also make him MUCH faster (outside of versus).
When running backwards and firing at the Tank, make sure you know where you're going. If you get stuck on the scenery and it's coming after you, you're probably screwed.
If the Tank is about to throw rubble in your direction, take cover unless you're sure you can pull off the zigzag method (i.e. running in one direction, then the opposite direction right after he throws the concrete). You can destroy thrown rubble by shooting it, but this is also unreliable without practice.
Best done in a campaign on easy with human players (AI's make no effort to avoid the Tank's thrown rocks.) When a Tank attacks, run away from it while focusing all fire on it. Tanks on easy will die in a matter of moments from concentrated gunfire.
Your health needs to be 40% or above to outrun the Tank. Try to be in an open space when faced with a Tank. If the Tank charges at you, run backwards as fast as you can but don't get separated from your teammates. If the Tank picks up some rubble, change your position. Try to engage the Tank with medium to long range weapon such as assault rifles. Nothing drops a Tank faster than Auto Shotguns at shorter ranges, but only use one if you're a competent backpedaler. Getting stuck on scenery or a wall while the Tank is coming for you means screwing up the achievement for everyone.
The achievement title may be a reference to the movie Ghostbusters.
This achievement is ludicrously easy on easy difficulty, where the Tank can be killed with only a focus fire from 3-4 Submachine Gun magazines.
"Tankbuster" is military slang for an anti-tank weapon.

 	NO SMOKING SECTION	(15G)
Kill 10 Smokers as they are pulling helpless Survivors.
You must shoot a Smoker to the death while it is actually dragging the Survivor, and before the Survivor is dragged into an obstacle or the Smoker itself.
"No Smoking Section" refers to an area in a public location, such as a restaurant, where smoking tobacco is not permitted.

 	HERO CLOSET	(10G)
Rescue a Survivor trapped in a closet.
This is an easy achievement to get. Once a Survivor dies, they will respawn in a closet. This happens after 1 minute, and after the rest of the Survivors move a certain distance from the dead body. Once the Survivor respawns, they will call out. They will have an orange outline while in a closet. Once found, open the closet to save them. This doesn't work if your teammate does it; you have to be the one to open the door.

 	HUNTER PUNTER	(10G)
Shove a Hunter off of a pinned and helpless Survivor.
You must free a pinned Survivor by using melee to hit the Hunter off him or her. You don't need to kill the Hunter, just melee him away.

 	101 CREMATIONS	(20G)
Set 101 Infected on fire.
Using molotovs or gas cans is the only way to gain this achievement. You must light 101 Infected on fire. Throw a Molotov in the path of a charging Horde to light them all on fire.
To set Infected on fire, you must throw a Molotov cocktail at them or light a gas can when they are near it. A gas can is recommended because of its large area of effect and longer burn. During a Panic Event, Crescendo Event, or a finale, throw the Molotov where the Infected are coming from, or in a central area, and you should get this achievement. Note that this is a cumulative achievement, which means that every time you burn an Infected, it adds up. You don't need to burn all 101 at once.
It is recommended to do this on Dead Air, in the first chapter. At the beginning there is always a big crowd behind the door and there are always four pipe bombs and four Molotov. First throw a Molotov in the greenhouse, then a pipe bomb in the flame. All Infected will run into the flames and that will count for the achievement.
This achievement's name is a parody of 101 Dalmatians.

 	TOWERING INFERNO	(10G)
Light a Tank on fire with a molotov
During most finales you will fight a Tank. Simply set it alight by either throwing a Molotov in its path, or shooting a gas can near it. This is easier to do in campaign; A.I. Tanks will do nothing to avoid a Molotov fire and will gladly charge right through it.
In the starting safe room of the No Mercy finale, there will be a Molotov. At least one Tank will spawn during a finale, although there are usually two. Simply throw the Molotov when the Tank is in a good position and the achievement will be earned. Try to throw a Molotov at him when he's climbing up something or throwing concrete.
The Towering Inferno is a movie about a skyscraper being set on fire.

 	TANK STUMBLE	(20G)
Stun a Tank with an explosion in the Crash Course campaign.
Pipe Bombs or a Propane tank will cause a Tank to stumble around, and doing so will unlock the achievement.
This achievement reuses the image from the Ground Cover achievement.
Shooting a Boomer next to a Tank will also stumble it but it is unknown if this counts toward the achievement.

 	WITCH HUNTER	(20G)
Kill a Witch without any Survivor taking damage from her.
If you get the Cr0wnd achievement, then you will also get this achievement. Focus on that achievement if you want both.
Startle a Witch from a distance and have everyone focus fire on her. If you do, she will likely die before reaching you.
Real life witch-hunters are still active to this day in some countries, but they peaked in activity between 1480 to 1700.

 	GROUND COVER	(30G)
Save another Survivor from a Special Infected while on the ground.
While on the ground, you must kill a Hunter or Smoker who has pinned someone, or kill a Special Infected who is in close enough proximity to another Survivor to count as protecting them. It is possible, though unlikely, to get this achievement by scoring the killing shot on a Tank.
Usually after being incapacitated, another Survivor will attempt to lift you back to your feet. It is very common that, while the Survivor is pulling you up, he or she may be pounced by a Hunter or pulled by a Smoker. As soon as you see this happen, begin blasting the Hunter or Smoker with your Pistol. The Special Infected will go down faster than you think, and the achievement will be yours. The reason this is not too easily earned is due to a small luck factor that affects it. This is because the chances of another Survivor being pounced or dragged is quite slim if you are in a group of good players. It happens often in Versus, since the Infected will focus on your teammate while he's helping you.
Another way to get this achievement is to throw a Molotov at your feet a few seconds before a Hunter pounces you. (Make sure it's actually targeting you and not another Survivor, or you'll just waste health.) The fire damage coupled with the Hunter mauling you should be enough to incapacitate you, and as long as no other Survivors interfere, the flames should kill the Hunter before you're killed, ironically giving you the achievement for saving yourself.

 	SPINAL TAP	(10G)
Kill an Infected with a single blow from behind.
When things are quiet, simply approach an Infected that has not yet noticed you and melee it in the back.
It is easier to attain this achievement in buildings and rooms where the Infected have a tendency to face the wall, leaving their backs open to an easy melee attack and subsequent kill.
An easy way to get this is to start on the Tunnel and head into the offices next to the saferoom. 2 or 3 Infected are almost always facing the wall in these rooms.
If a Survivor has been swarmed by a horde, run up to the swarm and melee the Infected in the back.
A spinal tap is a real life medical procedure to collect cerebrospinal fluids, which can aid in various diagnoses.
Spinal Tap is also a fictional band, subject of the 1984 mockumentary This Is Spinal Tap.

 	DEAD STOP	(10G)
Punch a Hunter as he is pouncing.
You must melee a Hunter as he is flying through the air.
Getting this achievement is a combination of luck and timing. Hit melee the instant before a pouncing Hunter reaches you.

 	BURN THE WITCH	(10G)
Light a Witch with a molotov.
Note that setting a Witch on fire will make her come after you, even if you didn't startle her. Normally, Witches leave after killing whoever startled them, but setting them on fire after they've killed their victim will send them into another frenzy. Therefore, attempt this achievement with care.
Simply throw a Molotov at a Witch as she is on the ground. Be ready, however, as she will still attack you while on fire.
She is more difficult to trick when on fire, so avoiding her is far more difficult.
She will, however, move slower when on fire, allowing you to run away without her catching up.
A burning Witch will only last for 15 seconds before dying.
This achievement is a reference to the Salem witch trials and witch-hunting in general.
This achievement shares it's name with an achievement in the Xbox 360 game, Banjo-Kazooie: Nuts 'n' Bolts where the player must fire a laser at the main antagonist of the game, who is a witch.
Note: This can also be achieved by lighting a Witch on fire with a gas can.

 	NO-ONE LEFT BEHIND	(20G)
Beat a campaign with all 4 Survivors.
This can be acquired on any campaign on any difficulty. During the finale, all four Survivors must get into the rescue vehicle.
This achievement may be a reference to the movie Blackhawk Down.
Due the nature of its finale, this achievement cannot be earned on The Sacrifice.
Possibly a reference to No Child Left Behind.

 	SMASH HIT	(25G)
Win a Versus campaign of Crash Course.
This is unlocked by simply winning any round of a Versus campaign in Crash Course.
This achievement is broken or glitched on the Xbox 360 and will only unlock if playing a versus game on a local server (see Crash Course notes section for information on forcing a versus game into a local server).

 	JUMP SHOT	(20G)
Headshot a Hunter while he's leaping.
Grab an Assault Rifle or Auto Shotgun, crouch down and fire full auto at the Hunter as it jumps toward you.
A jump shot is a basketball move, where you shoot the ball after you jump into the air. Here it's a play on that term: They jump, you shoot.
This achievement re-uses the picture on Dead Stop.
It's possible to earn this achievement without killing the Hunter as you only have to headshot it, not kill it.

 	CLEAN KILL	(10G)
Shove a Boomer and then kill him without him splashing on anyone.
This will usually require an open space. Melee the Boomer, retreat while he's stunned and shoot him. Note that meleeing the same Boomer too many times will make it explode all over you.
A clean kill is a term used by hunters and shooters to refer to a kill that was done with one hit and resulted in little blood being spilled.
It seems difficult to get this achievement in Campaign mode. Playing in Single Player grants this achievement easily.

 	QUICK POWER	(25G)
Restart the generator within 30 seconds of it shutting off in the Crash Course campaign.
This is acquired in the Crash Course Campaign, when the generator shuts off. Turning it on within 30 seconds will unlock this achievement.

 	DEAD GIVEAWAY	(10G)
Heal a fellow Survivor when your own health is below 10.
This can be frustrating to get in Single Player, as usually if your health falls below half, a Survivor Bot will heal you.
If you play with the Survivor Bots and you don't want them to heal you, select your first aid kit in your inventory. Having pill health and no permanent health will also count.

 	HELPING HAND	(20G)
Revive 50 incapacitated Survivors.
You only have to help Survivors onto their feet 50 times. You do NOT have to heal them.
Helping up Survivors incapacitated due to friendly fire still counts towards this achievement, even if your friendly fire caused them to be incapacitated. This can be easily abused to gain the achievement in single player mode.

 	BACK 2 HELP	(20G)
Leave a safe room to save an incapacitated teammate and bring them back safely.
Can be done on any difficulty except easy by downing a team mate while in the safe room, then helping them up as they are incapacitated outside of the room. (Note: This seems to have changed. Your ally must be downed by an Infected for this achievement to count).

 	PHARM-ASSIST	(20G)
Give pain pills to 10 Survivors.
Simply give your Pain pills to 10 Survivors. They must use the pills for it to count toward the achievement.

 	FIELD MEDIC	(20G)
Heal 25 Survivors with a first aid kit.
Self-explanatory. You can easily get this achievement in single player by starting a game, doing friendly fire damage to a teammate, and healing them.
If you really want to cheat, play through the first level of a campaign on Easy, take as little damage as possible, and make it to the saferoom. Ideally, your whole team will have first-aid kits. Now, switch the difficulty to normal or higher, shoot your teammates, and heal them with the full stock of first-aid kits. After that, restart the level, rinse, repeat.

 	CR0WND	(30G)
Kill a Witch with a single headshot.
Cr0wn simply means to kill a Witch without startling her. Because of this you can get cr0wned using the hunting rifle, contrary to popular belief. A shot to the head using the hunting rifle causes her to stumble, but she won't be startled until the stumble wears off. This gives you roughly 3 or 4 seconds to run over to her and melee her while shooting her. She will not be startled during all of this if you don't give her the chance to and you can get the achievement. See also: Modern Way To Kill Witch 2009
Sneak up right behind a Witch. She will not attack right away and slowly get up. Aim the shotgun right at her head. When she stands up and is about to be startled, shoot her right in the head. You will have some time to aim before she becomes startled, but don't take too long.
Don't go for this achievement if you are actually trying to beat the campaign. Play on single-player for the exclusive reason of earning this achievement. That way, you won't have to worry about screwing up.
With some luck, the Witch may spawn within sight and range of a mounted gun. With a little more luck, you can Cr0wn her by firing upon her with that mounted gun.
This achievement's name is a pun, but the basis of the pun is disputed. Some feel it is a combination of "crone" and "0wnd", other say it is a "1337" form of crowned.
An easy way to get this achievement, is to turn off your flashlight, sneak up behind the Witch and aim to the back of her head. As she is getting up (after looking up at you) shoot her in the back of the head, when she takes her eyes off of you, and turns back around, before she gets up.
Crouching can also improve accuracy, if using a shotgun. Try to follow her head as she starts to stand up, or aim for her chin. If you're not very good or are inexperienced at cr0wning, shoot more than once, just to make sure.

 	ZOMBIE GENOCIDEST	(20G)
Kill 53,595 Infected.
Play the game for a long enough time and you'll eventually get this one.
A quicker way to do this Achievement is to play through a finale as normal and then when the rescue vehicle arrives stay and hold out until you die while killing as many Infected as you can. It's best doing it in a glitches spot where the Infected cannot get you such as the "Jesus room," which is still unpatched on the 360 version.
This is a reference to the game Dead Rising, in which if you kill 53,594 zombies, it grants the "Zombie Genocider" achievement; Frank West, the player, has killed, down to a man, the entire population of Willamette. In order to outdo Dead Rising, Valve included this achievement and added one more to the kill count. The word is also a pun: the suffix "er" usually indicates something that is directly better than the previous (which is the ending of Genocider, although it's a different meaning in that term) while "est" indicates something that is the best. This Achievement is literally a "we are the best" statement.
This number is referenced in a set of safe house graffiti in the No Mercy campaign, with different inscriptions claiming 40, 50, 120 and finally "53,595!!!" zombie kills. This one in particular is underscored by the declaration: "LIES!!!"
Any kills done in split screen by a guest also adds to your kill count.
This achievement was later referenced by the game Prototype, which requires the player to kill 53,596 Infected in order to obtain the "Trail of Corpses" achievement.
In the Crash Course DLC, the achievement, 'The Littlest Genocide' also references this achievement, but with only 1/10 of the zombies required.
The easiest way to get this, is by going to The Terminal in the Dead Air campaign on expert, opening the door, and walking out, then back in to wait for the hordes that spawn after a bit.

 	MAN VS TANK	(30G)
Single-handedly kill a Tank.
Best done on easy single-player. Listen for the sounds of a Tank growling before the he actually attacks. Turn on your subtitles to help. When you hear the Tank, change the difficulty to expert and kill your AI companions to prevent interference. Change the difficulty back to easy and take on the Tank. With a Tier 2 weapon, a Survivor on his own won't have too much trouble taking the Tank down.
Set him on fire, don't let anyone shoot him, and just run away until he burns.
This achievement is a reference to the Unknown Rebel. It may also be a reference to the TV show Man vs. Wild.
During the finale of The Sacrifice, the player sacrificing themselves may get this achievement. It is unknown whether it is a glitch or if intended by Valve, seeing as Bill took on three Tanks shortly before his death in The Sacrifice comic.

 	THE LITTLEST GENOCIDE	(25G)
Kill 5,359 Infected in the Crash Course campaign.
This is unlocked by killing 5,359 Infected within the two maps of the Crash Course campaign.
This is an obvious reference to the Zombie Genocidest achievement.
This achievement requires only 1/10 of the zombies required in the Zombie Genocidest, but it has a larger reward.

 	UNTOUCHABLES	(30G)
No Survivors take damage after contacting the rescue vehicle.
There are glitches which can help with this achievement. See the finale pages to get more tactics.
A good way to get this achievement on the Xbox 360 is to go to the finale on the Dead Air campaign and stand in the back of the map on the left corner. The bots should take care of all Infected, leaving the human player(s) completely safe.
It no longer works on the PC, but the glitch is still available in the Xbox 360 version. It can make the No Mercy finale much easier.

 	RED MIST	(20G)
Kill 1000 Infected with a mounted machine gun.
In finales & Crescendo Event, there is usually a mounted Minigun. Use it as frequently as possible.
There are miniguns at each finale except for Blood Harvest, along with certain crescendo events. These are the first crescendo event in No Mercy, and the third crescendo event in Death Toll. Use these miniguns enough and you will gain this achievement. A somewhat useful trick is to throw a pipe bomb in front of the line of sight of the minigun and kill the infected that gather.
"Red mist" a term for a cloud of blood.

Full Campaign Achievements
 	STOMACH UPSET	(20G)
All Survivors complete a campaign without being vomited on.
This is a combination of luck, skill and subtle mathematical use.
Always hit nothing but melee if you hear a Boomer. All it takes is one trigger-happy Survivor to ruin it for everyone.
The name of this achievement is a play on the term "upset stomach", a term often used to describe nausea, which is a common cause of vomiting.
It is highly likely that restarting a campaign in-game instead of the lobby will count as one large campiagn, frustratingly nullifying the achievement.

 	SAFETY FIRST	(30G)
Play an entire campaign with no Survivors taking friendly fire damage.
Although friendly fire does not cause damage on easy, it still registers as friendly fire and the achievement will not be unlocked.
When a Survivor is surrounded, allow him to help himself, or use melees to assist him.
This can be easily done on a campaign where the other three players are bots, because they won't cause friendly-fire damage from firearms. However a bot can cause friendly fire damage if one accidentally sets off a gas can or propane tank next to the player. So just as long as you avoid hitting the bots, and stand clear of explosive items, you'll get the achievement.
This can also be done by 4 players meleeing through the entire campaign, although it is impossible to deal with the Tank head-on in this way.
An alternative way is to play through a Single Player campaign in Easy, then melee through the entire campaign.
The image of the achievement might be a hint to use the Hunting Rifle as it is more precise than the other full auto weapons and has less chance of hitting another Survivor.
While it is very rare, bots do have the ability to have a stray bullet hit a gas can or propane tank and the explosion will hurt you and count as friendly fire. Destroy the items preemptively or move them so the bots can't shoot it by mistake.

 	DO NOT DISTURB	(20G)
Sneak past all Witches in a campaign without disturbing one.
This only requires you to get through ONE campaign without startling a Witch. Simply listen for the signs on a Witch. Cr0wning her will not count as startling her. Only when it says "x has startled the Witch" will it count against the achievement. If she is directly in your way, have one-two people run by her at a time.
Play on Easy. There will be some instances where a Witch is literally sitting IN a doorway you must pass through, and cr0wning will be necessary. Cr0wning is obviously easiest to do on easy.

 	ZOMBICIDAL MANIAC	(30G)
Survive any campaign on Expert.
"Simply" survive one campaign on expert to get these achievements.
Only the Survivors who make it to the rescue vehicle will get this achievement.

 	STAND TALL	(20G)
Survive a campaign without being incapacitated.
This can be done on any difficulty, so play on Easy if you're specifically going for this one. It's very doable in single player, but having a good human-controlled team practically makes this achievement guaranteed.

 	WHAT ARE YOU TRYING TO PROVE?	(35G)
Survive all campaigns on Expert.
"Simply" complete all the campaigns on expert to get this achievement.
A 'cheat' for this is to play campaign online with more than 2 Players at least and then do Chapters 1-4 on a campaign on Easy; then when you're at the finale, don't open the saferoom door and vote to return to lobby and change the chapter of the campaign you were doing to the Finale and the difficulty to Expert and then you only need to finish the finale on expert and not the whole Campaign.
This may also be an easter egg to Valve's popular game, Half-Life 2, where the antagonist Wallace Breen asks the silent protagonist Gordon Freeman, "What are you trying to prove?", since the player must go through many hardships to survive.

 	UNBREAKABLE	(30G)
Finish a campaign without being healed by a first aid kit.
Being healed by another Survivor counts as being healed.
Note that you CAN consume pain pills.
If you attempt this with AI players who then try to heal you, in order to cancel this, select a First aid kit you have in your inventory, otherwise there is no way to stop the AI from healing you. However, you will have to constantly stop and do this, every few moments. It is generally a much better idea to do the achievement with human players and on lower difficulties.
If you are playing an online campaign, going idle before the heal process completes will allow you to be healed, but won't count against the achievement. This way, you can be healed and still get Unbreakable.
If you have low health and you are near the end of the level you can have a human partner kill you so you come back with 50 health (if you die in a safehouse all your supplies will carry over to the next level as long as they are IN the safehouse).
If you are at the finale and are incapped, as long as you don't die before everyone else reaches the Rescue vehicle, the achievement is still unlocked.
The achievement's name may be a reference to the film Unbreakable staring Bruce Willis playing the role of a man who never requires medical treatment due to self-healing powers.

 	NOTHING SPECIAL	(30G)
Survive a campaign with no Survivors taking damage from Special Infected.
Special Infected are usually very tenacious, so use your weapons with equal tenacity.
It is possible to do this on Versus Mode, just gather up a group of friends and when playing as Infected, do not harm the Survivors in any way. Unless there has been an update this has been confirmed to work on Crash Course in Versus. It is possible that it would work on other campaigns but Crash Course is much easier to complete as it is only 2 chapters.
Killing oneself in order to restart a chapter will not reset the status of this achievement. The campaign must be done from lobby to finale with no Special Infected damage taken.
Witches don't count as Special Infected for this achievement.
An easy way to get this achievement (only works on 360 Version) is to play campaign online with recommended of 1-3 other players and then do Chapters 1-4 on a campaign on any difficulty (Easy difficulty recommended) and when at the Finale don't open the safe room door (or it'll mess it up) and have everyone vote to return to lobby. When at the lobby the Host of the room changes the Chapter of the campaign you were doing to the Finale. Then when the game is started; this is when you can't take damage from Special Infected; so basically its only surviving the campaign on the Finale without any Survivors taking damage from Special Infected and not the whole campaign.
Another way to achieve this on the Xbox 360 is to get to the Runway Finale on Dead Air on Easy difficulty. Have the Survivors use two Assault Rifles and two Auto Shotguns (thus, the player should play as Zoey so her Bot AI doesn't use the Hunting Rifle). Clear all of the Infected, and stock up before activating the rescue. Run past the large aircraft parked in front of the C-130 Hercules plane, all the way until you are touching what appears to be police line tape. From there, the horde will primarily come from in front of the Survivors but have spawned from behind the tape as well as down the broken aircraft shaft to the right. Special Infected will spawn while on the tape but will not engage or advance to the Survivors with the exception of the Tank until you make your run back to the C130 during the escape. The first Tank will usually get stuck on the opposite side of the large aircraft making it an easy and relatively effortless target to down. The second Tank will come from just to the right of the large aircaft over a nearby truck. Keep in mind this tank will throw chunks of earth before reaching the Survivors. This method helps earn NOTHING SPECIAL and UNTOUCHABLES Achievements simultaneously. It may take several tries to accomplish this. As of 5 January 2011 the glitches in this method has not been patched.

 	AKIMBO ASSASSIN	(30G)
Survive an entire campaign using only pistols.
You may use single or dual pistols. You can use environmental advantages but you cannot use primary weapons or the minigun.
In order to prevent accidental firing of a primary weapon, do not pick one up. This is especially useful after using a First aid kit, consuming pain pills, or being revived, as after these actions have finished, you automatically revert to selecting your primary weapon which could lead to accidental firing, especially during intense situations.
Molotovs and Pipe bombs may still be used.
Use pistols to your advantage since when crouching they have very high accuracy and which they can take out Smokers or Boomers from quite a distance away.
When you are forced to fight a Tank or a Witch, let the bots take care of them. Stay out of the way and avoid engaging them, as the pistols are not powerful against either of them if they close in.
Although its original meaning is starkly different, dual wielding is sometimes called akimbo style.
An easy way to get this Achievement is to play through No Mercy on easy and stay low when a Tank spawns.
When playing online, make sure your team doesn't mind before you attempt this achievement. It's just common courtesy (and it will probably keep you from being kicked).
Another way to get this is to go on Single Player Mode and do it. AI primary fire will not mess up you getting this achievement. Only YOU have to survive the campaign only using pistols, not AI.

Versus Mode
 	DOUBLE JUMP	(20G)
Pounce two different Survivors in one life as a Hunter.
This is down mostly to the eventual lucky opportunity of being a Survivor using their melee attack to get you off a Survivor. You then need to get away without being killed. It works the best to wait for the Survivors to get separated; and then pounce on the lone one. As soon as they're dead, flee to avoid the other Survivors. The next time you pounce, you will get the achievement.
You can also pounce on a Survivor in a group and hope to be punted off without being shot to death afterward. Then simply step back and pounce again.
A double jump is a common skill in many video games, it allows a person to jump in the air.

 	JUMPIN' JACK SMASH	(25G)
Pounce a Survivor for 25 points of damage in the Crash Course campaign.
Getting a 25 can sometimes prove difficult, however sticking to high places is the best place. Remember that the Hunter arcs in flight, so aim a little higher.
This is a reference to the song Jumpin' Jack Flash by The Rolling Stones.
This is a broken or glitched achievement on the Xbox 360 and will only unlock if playing a versus game on a local server (See Crash Course Campaign wikia page for information on forcing game into local server).
Easy way to do this, set up versus friends only with two controllers and bots (guest should be a survivor) and force game onto a local server. Grab the second controller and using the shot gun, incap and kill the three survivor bots. In front of the nose of the downed helicopter, there is a guardrail that looks almost like a border for the "safe area". Position the Survivor on the opposite side of the guardrail from the downed helicopter and towards the beginning of the guardrail. As an infected, you should start out as a smoker, run into the line of sight of the survivor and then switch controllers and kill the smoker. You will then spawn as a boomer and need to repeat what you have just done. You should now spawn as a hunter. Climb up to the roof of the warehouse behind the tail of the helicopter. There should be a chimney/smokestack that overlooks the "safe area." Climb on top and crouch. This next part will take some practice and correct judging. Since you are on the high ground, you want to set up the jump in order to land directly on the survivor at that height. If you aim directly at the survivor and jump, you'll come up short. You have to aim at a spot above a survivor. You should be aiming a little high than the skyline of the city off in the distance. If you arc it correctly, you should cause 25 points of damage and unlock the achievement.

 	CHAIN SMOKER	(20G)
Constrict two Survivors in one life as a Smoker.
The strategy is largely the same as double jump. You need to hold on to the Survivors long enough to cause damage.
Stay on the rooftops. When someone is freed, back away from the roof edges to avoid gunfire. When the Survivors forget about you, constrict someone again.
A chain smoker is a person that has a habit of smoking multiple cigarettes in succession, usually one right after the other.

 	BIG DRAG	(20G)
Drag a Survivor 100 feet with your tongue as a Smoker.
Spawn behind the group and nab the Survivor in the back. Eventually you will get lucky enough to have the Survivors not notice, and you will survive long enough to get the achievement.
This can also easily be done by hiding among the trees in the first section of Blood Harvest, as you will rarely be spotted before you grab a Survivor and long distances are abundant.
Pull a survivor right into a pipe bomb. The explosion will do good damage to your victim and also add distance to the pull.
Big Drag is a play on words, referring to both the act of dragging a survivor, and taking a drag from a cigarette.

 	SLIPPERY PULL	(25G)
Smoker pull a bile-covered Survivor until you hold him during Crash Course.
Once a Boomer pukes on any Survivor, simply pull him with your tongue and the achievement will unlock.
This Achievement is broken or glitched on the Xbox 360 and cannot be unlocked if playing on a dedicated server. It can be unlocked offline via system link or online using a local server (see Crash Course notes section for directions on forcing a versus game into a local server).
NOTE: Using system link is extremely difficult and not recommended.

 	DEAD WRECKENING	(20G)
Dole out 5000 total Survivor damage as a Special Infected.
Simply play versus long enough and you're bound to get it.
This achievement is a reference to the vehicle used in Land of the Dead by the mercenaries in the film. The vehicle's name was Dead Reckoning.
A way to get the Achievement faster is when you get the chance to play as a Tank try and bash out as much from the Survivors and try and incapacitate them and then go for the rest of them and you should get 25 damage per punch as a Tank.

 	BARF BAGGED	(20G)
Cover four Survivors with Boomer bile at once.
Exploding on Survivors doesn't count. You must vomit on all 4 in one attack.
Vomit on all four of the Survivors at once. If even one is missed, you will not get the achievement. One of the most important things to remember when trying to get this achievement is "location, location, location". If the Survivors are huddled into one corner, go for it.
Remember that if the Survivors are huddled too close, it will be tricky to hit the ones at the back of the group. Another tactic to avoid this situation is to look for an opportunity to ambush the Survivors when they are very slightly spread out, and spraying them all with bile in one horizontal motion.
A "barf bag" is a slang term for the air sickness bags provided on most airlines, intended for passengers that get sick during the flight to vomit into.

 	ALL 4 DEAD	(30G)
Incapacitate or kill all four Survivors in one life as a Tank.
This is down to your individual tactics.
Getting hit by a car instantly incapacitates a Survivor. If you can knock a car down a narrow hallway as all four Survivors are together, you can knock them all out in a single hit.
This achievement tends to be easier to get in the beginning of a campaign when the Survivors have only the pump shotgun and submachine gun, as they do much less damage to a Tank than the auto-shotgun, assault rifle, or hunting rifle that tend to be found later in a campaign, but obviously this depends on what items are spawned by the AI Director and in what location. Just keep playing Versus, hope you get to become a Tank early in the game, and just keep attacking and you can earn this achievement.
Although it's something that can be frowned upon normally, you can "steal" kills from team mates who have constricted or pounced players that are not yet incapacitated.
Note that as the Tank it is you that needs to incapacitate each survivor to earn this achievement, if you incapacitate three Survivors and a team mate incapacitates the last one you do NOT receive this achievement.
Likely a play on the phrase "One for all, and all for one." Could also be a reference to the game's title.

 	LAMB 2 SLAUGHTER	(20G)
As an Infected, incapacitate a Survivor who has entered and left a safe room.
This is down to your individual tactics.
It is possible that pouncing a Survivor as Hunter just as they close the door can earn you this achievement.
One of the easiest ways to do this is to wait outside the door after someone decided to go Rambo and run to the safe room without their teammates.
Another way to do this is use a Smoker to drag a Survivor out of the safe room and incapacitate him/her. You may have to choose a Survivor low on health to incapacitate him/her before other Survivors come.

 	20 CAR PILE-UP	(20G)
As a Tank hit 20 Survivors with a car in the Crash Course campaign.
This achievement is cumulative, so it is not all in one game. The best place to get this will be the parking lot with the alarmed cars.
Dumpsters also affect the progress of this achievement.
On the Xbox 360: Hitting Survivors with a car does not count towards the achievement when playing on a local server. You must play on a dedicated server in order to receive credit. Interestingly, this is exactly opposite of the numerous broken versus achievements for Crash Course.

 	TRUCK STOP	(35G)
Your team wipes all Survivors after the escape vehicle has opened in Crash Course.
Simply incapacitate all the (remaining) Survivors after the escape vehicle appears in the Crash Course campaign. Probably easiest by being the Tank that spawns when the vehicle has arrived.

 	WIPEFEST	(35G)
Your team incapacitates three Survivors within five seconds in the Crash Course campaign.
To earn this achievement you or your team 'simply' need to incapacitate 3 Survivors within 5 seconds of each other. The easiest way of achieving this is having a Tank incapacitate multiple Survivors in one go by hitting a car/forklift/object at them.
You must be one of the 3 Infected players incapacitating a Survivor player to be awarded the achievement.
You can get this achievement as a survivor using the following scenario (This is confirmed to work). Set up a versus friends-only game hosted on a local server using two controllers and bots (See Crash Course Campaign wikia page for explanation on forcing game into local server). Make sure the 2nd player guest is a survivor, and primary account is an infected. After the game has loaded, do not spawn as an infected. Using the second controller, do not leave the safe area. Grab the shot gun and shoot a survivor bot until they start to heal themselves. When a bot starts to heal him or herself, repeat the process with a different bot until all three bots have used their health packs. Now, shoot each survivor until their health is just above the point of incapacitation. Now, all you have to do is shoot the three bots and incap them all within 5 seconds and the achievement unlocks for the host account.

PC Exclusive
Survival Mode
None of the Survival Achievements are present in the Xbox 360 version of the game since it is free DLC.
 	BRONZE METTLE
Earn a Bronze medal in Survival mode on any official level.
It is a pun on the word "medal" and "mettle".

 	SILVER BULLETS
Earn a Silver medal in Survival mode on any official level.
A common myth is that silver bullets are effective in slaying werewolves. Less common myths are that silver bullets will also kill or highly damage vampires and zombies.

 	VIOLENCE IS GOLDEN
Earn a Gold medal in Survival mode on any official level.
A play on words of the term "silence is golden."

 	DISTINGUISHED SURVIVOR
Earn at least a Bronze medal on every official Survival level.

 	HEROIC SURVIVOR
Earn at least a Silver medal on every official Survival level.

 	LEGENDARY SURVIVOR
Earn a Gold medal on every official Survival level.

 	LAST STAND
Complete one round of Survival on The Last Stand.

Miscellaneous
Achievements that don't fit anywhere else.
 	OUTBREAK
Catch a rare strain of infection, then pass it on to someone else.
This is unlocked by being vomited on by a player-controlled Boomer who already has this achievement, while in Versus
This achievement originated from Boomers controlled by Valve developer players.

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