Shields come in three basic varieties: Light shield, Heavy shield and Tower shield. (Spiked shields and Bucklers were not implemented in NWN2). You strap a shield to your forearm and grip it with your hand. When using a shield you must grip your weapon (if any) with only one hand.
- Shields grant a shield bonus to the wearer's armor class. This number represents the protective value of the shield. The bonus does not stack with other effects that grant a shield bonus. The Shield (spell) grants Shield Enhancement AC, which does not stack with enhancement bonus of a shield, but it does stack with its base AC.
- Shields have an armor check penalty.
- Unlike in D&D 3.5, you CANNOT make a bash attack with shields. You also cannot equip a shield without the appropriate Shield proficiency feat.
D&D 3.5 comparison
You could make a bash attack with all shields, except bucklers. Spiked shields are specifically for bashing and cause extra damage.
Finally, the Buckler could be used with bows and crossbows without penalty, and with two-hand or off-hand weapons with a -1 attack penalty.