XCOM: Enemy Unknown

Earth First (Difficulty)
Beat the game on Classic difficulty.

Our Finest Hour (Difficulty)

Beat the game on Impossible difficulty.

No Looking Back (Difficulty)
Beat the game in Ironman Mode on Classic or Impossible difficulty.

A Continental Fellow
Win the game from each of the 5 starting locations.

Lone Wolf (Difficulty)
Clear a UFO Crash Site with one Soldier on Classic or Impossible difficulty.

Wet Work (Difficulty)
Complete a Very Difficult abduction mission in five turns or less on Classic or Impossible difficulty.

Shooting Stars
Shoot down 40 UFOs.

Meet New People. Then Kill Them.
Win a multiplayer match.

Bubonic
Play a multiplayer match against someone with this achievement.

Zom-B-Gone (Story)
Eradicate the infestation

An Army of Four (Difficulty)
Beat the game without buying a Squad Size upgrade(Classic+ difficulty)