Classes represent chosen professions taken by characters and some other creatures. Classes give a host of bonuses and allow characters to take actions that they otherwise could not, such as casting spells or changing shape. As a creature gains levels in a given class, it gains new, more powerful abilities. Most PCs gain levels in the core classes or prestige classes, since these are the most powerful. Most NPCs gain levels in NPC classes, which are less powerful (see Creating NPCs).