Shield Proficiency( Player's Handbook v.3.5, p. 100)
You are proficient with bucklers, small shields, and large shields.
You can use a shield and take only the standard penalties (see Table 7—6: Armor and Shields, page 123).
Barbarians, bards, clerics, druids, fighters, paladins, and rangers automatically have Shield Proficiency as a bonus feat. They need not select it.
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.