Combat Expertise [General]
You are trained at using your combat skill for defense as well as offense.
When you use the attack action or full attack action in melee, you can take a penalty of as much as -5 on your attack roll and add the same number 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.
A character without combat expertise feat can fight defensively while using the attack action or full attack action to take a -4 penalty on attack rolls and gains a + dodge bonus to armor class.
A fighter may choose combat expertise as one of his fighter bonus feats.