Healing is something of an anomaly amongst the schools of magic given that most fantasy systems tend to put it into the category of "things that magic doesn't do" and give that job to whatever the system uses by way of theurgy instead.
Needless to say, this is "somewhat" at odds with real world magical practices - for which healing is usually a key objective. The most likely explanation is the old bugbears of "game balance" and "niche protection".
Where healing is available to magicians, the mechanism by which it works will still need to be examined - it may be a school in its own right, specialising in zapping away hitpoint damage, or perhaps a "white" branch of necromancy that deals with "positive life energies". If it resembles medicine and requires hard work and time to effect a cure then it may be related to biothaumaturgy or a branch of alchemy. Shamen, ward-magicians or abjurers may be called upon to drive off "disease spirits" or invokers may bring up helpful ones.
Generally healing will be required to deal with three basic sets of problems - traumatic injuries, poisons and diseases (or, in gamist terms, hitpoint damage, cycling attacks and status effects/debuffs). There may or may not be different cures for each and it will effect the feel of the system a lot depending on how they work - a system in which wounds can be instantly and painlessly zapped away in real time is likely to be far more combat happy than one in which healing magic means a ritual to ensure that the wound heals naturally without infection or scarring. Likewise a disease or poison that can be zapped off is a lot less threatening than one that takes days of campaign time to cure.
The availability of supernatural healing, whether magical or theurgical may also be expected to have an impact on the campaign setting1.
In extremis healing magic may even include resurrection - indeed it is not entirely unknown for this to occur even in systems where there is no other form of magical healing. This is often your darker and edgier form of resurrection with a significant chance that the resurectee will "come back wrong" or there will be some other form of related trouble. In fact in this whole general vein some systems may differentiate between magical and theurgical healing by making the magical form darker and edgier (or at least messier and slower), requiring surgery and the use of magical medicines rather than instant and miraculous cures.
Magically assisted surgery may occasionally be referred to as chirurgy. Some settings may require some medical understanding before magic can be used for healing - in this case, magic can heal but the user has to know what he wants to achieve before it will work2. This may make simple trauma surgery relatively easy ("I want to join this side of the cut to that side") but treating a disease requires an understanding of what is causing it (and if you don't understand germ theory, you are whistling in the dark). Here, theurgy may be simply better at healing because whatever you are invoking is better at human biology than you are.
- The False Face Society - an Amerindian organisation which uses shamanistic practices centred around a set of fetish masks to heal.
Game and Story Use
- Who can deliver magical healing and how will have a significant effect on your campaign.
- How effective and how quick magical healing is can have effects on the game's lethality… and not always in obvious ways. If healing can get someone back up and into fighting condition quickly, the enemy suddenly has a very good reason to confirm their kills. If it just stabilizes its target while not healing them enough to continue fighting, or is only useful after the fight's over, it makes more sense for an enemy to focus on active threats instead of finishing off the wounded.