-----Counterspells

--How Counterspells Work
To counterspell, you must select an opponent as the target of the counterspell. You do this by choosing the ready action. In doing so, you elect to wait to complete your action until your opponent tries to cast a spell. (You may still move your speed, since ready is a standard action.)

If the target of your counterspell tries to cast a spell, make a Spellcraft check (DC 15 + the spell’s level). This check is a free action. If the check suceeds, you correctly identify the opponent’s spell and can attempt to counter it. If the check fails, you can’t do either of these things.

Make a a Caster Level check (DC 10 + opponent’s caster level + spell level). If this check succeeds, make a Concentration check opposed by the defender’s Concentration or Caster Level check (whichever has the higher modifier). If you win, the spell is counterspelled. If you lose, the spell is cast successfully.

--Counterspelling Metamagic Spells
Metamagie feats are not taken into account when determining whether a spell can be countered.

--Specific Spells as a Counterspell
Following a successful Spellcraft check to identify the spell being cast, you may instead elect to cast the same spell as your opponent. If you are able to cast the same spell and you have it prepares, you cast it, altering it slightly to create a counterspell effect. Both spells automatically negate each other with no results.

--Dispel Magic as a Counterspell
You can use dispel magic to counterspell another spellcaster, and you don’t need to identify the spell he or she is casting. However, dispel magic doesn’t always work as a counterspell.

--Specific Exceptions
Some spells specifically counter each other, especially when the have diametrically opposed effects.

---Improved Counterspell [General]

--Benefit
When counterspelling, you gain a +4 bonus on the opposed check you make to counterspell your opponent.

--Special
A wizard, sorcerer, or cleric may select Improved Counterspell as one of his bonus feats.

---Quick Counterspell [General]

--Prerequisites
Caster Level 5

--Benefit
Once per round, you may initiate a counterspell as an immediate action.

--Normal
Counterspelling requires a readied action