"Transfiguration is the most complicated and dangerous spell in your Hogwarts course. If anyone wants to be naughty in my class, I'll ask him out and never let him come back. I warned you. "

-Minerva McGonagall, the first freshman lesson (chapter 8 of the Sorcerer's Stone).

Professor McGonagall teaches transfiguration at Hogwarts, and so does President Dumbledore.

Transfiguration is the magic of changing one object into another. It can turn inanimate objects into living things, and vice versa. Some deformation spells can change a certain part of things, for example, a person's ear can become a rabbit's ear. At Hogwarts School of Wizardry, Metamorphosis is taught by Professor McGonagall. Fifty years ago, Dumbledore was a perverted teacher at Hogwarts (the Chamber of Secrets). The transfiguration spell has been used in ancient times. Circe, a witch who lives on the Greek island of Ayu, is famous for turning a lost sailor into a pig (Chamber of Secrets/Games).

Contrary to deformation, it is irreversible and non-deformation, which can change the deformed object back to its original shape (Order of the Phoenix, Chapter 29).