Is there a limit for the number of class/prestige classes a PC can take?
From D&D Wiki
I have a player that wishes to acquire another class, this one a prestige class, but she already has three classes, so I wasn't sure if there was a set limit or not, any ideas?
 Ghostwheel 08:15, 11 August 2009 (MDT)
No, by the rules there is no limit or prestige classes, or classes you can take for that matter.
There is the experience point cost limit if base classes (not counting favored) are not within 2 levels of each other. For example, say a player chooses a human as his race. He takes 6 levels of wizard, and 4 of bard. Because humans have any class as their favored class, the penalty does not apply, but if the player takes another base class, say ranger, he takes the penalty of 20% experience until bard and ranger are within 2 levels of each other. It is not a hard limit, but it should discourage too much base class mutliclassing, as the effects are cumulative. Another new base class (say monk), and the player is taking a 40% penalty. This doesn't apply for prestige classes though. Players can have any amount of those, as long as they don't have conflicting classes.
 Ghostwheel 10:04, 11 August 2009 (MDT)
And this is why multiclassing shouldn't be punished, and why the XP penalty rules are dumb.