3e SRD:Combat Reflexes
From D&D Wiki
|This material is published under the OGL|
Combat Reflexes [General]
Benefit: When foes leave themselves open, the character may make a number of additional attacks of opportunity equal to the character's Dexterity modifier. The character still may only make one attack of opportunity per enemy. The character may also make attacks of opportunity while flat-footed.
Special: A rogue with the Combat Reflexes feat still can only make one attack of opportunity in a round if he uses his opportunist ability to make that attack.