Multi-class characters in D&D were awesome, but extremely difficult to play as you had to abandon one class for the next and concentrate on that new class at the expense of the other. This was more trouble than it was worth and usually the only multi-class characters you ever came across were NPCs. With the Third Edition rules, Wizards of the Coast has made a considerable rule change, allowing players to add a new class at every level. For instance, if you're a level one fighter and get enough experience to move up to level two, you can now opt to add a Cleric level instead. More importantly, there is no penalty for changing or adding classes. This alone will really open up the game, allowing characters with varied skills and abilities at a much faster rate.