You are proficient with bucklers, small shields, and large shields.
Benefit: You can use a shield and take only the standard penalties (see the Armor and Shields table).
Normal: When you are using a shield with which you are not proficient, you take the shield’s armor check penalty on attack rolls and on all skill checks that involve moving, including Ride checks.
Special: Barbarians, bards, clerics, druids, fighters, paladins, and rangers automatically have Shield Proficiency as a bonus feat. They need not select it. Classes added after the Player’s Handbook (version 3.5) may also automatically have this feat; check the Weapon and Armor Proficiency section under Class Features for the character class in question.
Source: Player’s Handbook (version 3.5), page 100.