Concentration

Concentration (CON)
Allows you a chance to continue casting a spell after being damaged or otherwise interrupted. When you take damage you roll a D20 + your Concentration score against a difficulty class of 10 + the damage received + the level of the spell you are trying to cast.

This skill is also important for monks as their ability to retain Ki is tied to Concentration.

Class Skill
for Bard, Cleric, Favored Soul, Monk, Paladin, Ranger, Sorcerer, Wizard