Armor & Weapon Proficiency
The weapons and armor a character can use without penalty is determined by their class. At first level each class is proficient using certain types of armor and weapons. Some races confer additional proficiencies and players seeking additional armor and weapon proficiencies for their characters may use Feats or look to prestige classes which bestow those proficiencies. Characters attempting to use a weapon they are not proficient with suffer a -4 penalty on to-hit rolls; while players using armor they are not proficient with suffer penalties in combat and while using skills involving physical movement. To determine the severity of the penalty consult the Armor and Shields table and look for the Armor Check Penalty column. This amount is subtracted from any to-hit roll, Reflex saving throw, or skill check involving a Strength-based or Dexterity-based skill. Non-proficiency penalties for armor and shields stack, so a character both a breastplate and using a tower shield she was not proficient with would suffer a -14 (minus 4 for the armor and minus 10 for the tower shield) penalty to all to-hit rolls, Reflex saving throws, and active skill checks.
See individual character class descriptions for full information about which weapons and armors those classes begin proficient in. Characters may purchase feats which confer additional weapon or armor proficiencies.