Improved Trip [General]
Prerequisites: Int 13, Combat Expertise.
Benefit: You do not provoke an attack of opportunity when you attempt to trip an opponent while you are unarmed. You also gain a +4 bonus on your Strength check to trip your opponent.
If you trip an opponent in melee combat, you immediately get a melee attack against that opponent as if you hadn't used your attack for the trip attempt.
Normal: Without this feat, you provoke an attack of opportunity when you attempt to trip an opponent while you are unarmed.
Special: At 6th level, a monk may select Improved Trip as a bonus feat, even if she does not have the prerequisites.
A fighter may select Improved Trip as one of his fighter bonus feats.
Source: SRD 3.5 Feats