Dungeons & Dragons Online uses a modified version of the spellpoint system presented in the Unearthed Arcana rulebook. Spellcasters receive a number of spellpoints based on character class, ability scores, and other factors. Spellpoints are expended whenever a spell is cast, and are restored by resting.
Wizards and clerics must memorize a limited selection of their known spells; they can cast a memorized spell as many times as they want, as long as they have the spellpoints to do so. Sorcerers and bards can cast any spell they know until they run out of spellpoints.