In addition to the kinds of restrictions normally required by subclasses, Prestige Classes often require that a character have ranks in particular skills, abilities, feats or spellcasting ability. The role-play effect in the game is not so much that of changing careers (as with dual classing) or combining multiple classes, but more like achieving recognition in the character's original class or classes and being allowed to join an exclusive brotherhood of similarly skilled individuals.
Many Prestige Classes are focused on specific goals and require that the character act accordingly. Other classes are focused on a specific set of abilities.
