From D&D Wiki
|This material is published under the OGL|
Combat Expertise [General]
When you use the attack action or the full attack action in melee, you can take a penalty of as much as –5 on your attack roll and add the same number (+5 or less) as a dodge bonus to your Armor Class. This number may not exceed your base attack bonus. The changes to attack rolls and Armor Class last until your next action.