Blue mages in "Final Fantasy XI" are a class of mage that specialize in blue magic. Blue magic differs from other types in that the spells are learned from monsters instead of the typical scrolls.
Blue magic can only be learned by defeating a monster after it has used a learnable ability. It cannot be learned if the specific blue magic ability exceeds the character's level. Also unique to blue mages is the concept of "setting." Blue magic cannot be used as soon as it is learned. Rather, one must use points to allocate a certain number of spells to the character. This means that a character can only have a certain number of blue magic spells set at any given time.