There are Six Laws of Magic. Breaking these metaphysical laws causes the life energy of magic to rebound against the caster, driving them slowly but surely crazy. The first two are sometimes called the Lesser Laws, as there are ways around them, but the second set of four, also known as the Greater Laws, are inviolate.

Permanently enchanted items are not subject to the First and Second Laws of Magic. The necessary rituals to permanently place magic within an item provide a buffer between the caster and the effect, and items lack the metaphysical qualities necessary for corruption to take hold of the item itself. The Greater Laws still cause corruption if cast through a magic item.

As the legends of the Dread Emperor Karsen and the Luminals have them regularly breaking these laws, it is not known if they are all thoroughly insane or have some method of staying sane while violating the Greater Laws.

I You shall not harm the living with magic.
This is a prohibition against both direct harm and immediate indirect harm: injuring someone by damaging the walls of a building so it collapses on them, or levitating an item over their head and letting gravity do the work, is still harm. Burning down a field and causing people to starve is not harm since the consequence is too removed from the action. Increasing someone's strength, even if that person then beats up someone else, is also allowed.
This prohibition only applies to sapient creatures of the natural world, though. Animals, demons, the undead, and elementals can be harmed without breaking the law.
This is also only a prohibition against physical or mental injury. Restraining someone with magic is allowed, even if mundane forces are coming to cut off his head.
II You shall not alter the form of another grossly, involuntarily, or permanently.
You can't turn people into toads or trolls, with or without their permission. Nor can you use magic to mutate the living.
You can make changes to the forms of volunteers for a few hours. You can double or halve their size, give them gills or cats eyes, and use similar effects that keep their basic form the same.
You can change yourself however you want.
III You shall not bend the minds of the living to your will.
All forms of direct mind-control are prohibited against natural, seapient beings. Summoning or controlling animals or elementals is allowed. Minor effects, such as sleep, fear, dazing, or stunning, are allowed.
IV You shall not disturb the sleep eternal.
This is a blanket prohibition against all forms of necromancy: creating undead, summoning undead, or controlling undead. It doesn't matter what form the undead are: skeletons of animals, skull spirits, vampires, mummies, wraiths, or whatever else. Resurrection and reincarnation also forbidden.
Destroying undead and chasing them away are allowed.
V You shall not swim against the flow of time.
Stopping time, traveling to the past, or jumping to the future is not allowed. Speeding up or slowing the passage of time is allowed.
Divination is allowed.
VI You shall not disturb the Outer Gates.
Summoning demons and Elder Things is strictly forbidden. Elementals do not count as demons and can be summoned and controlled.