Transformation is a category of magical effect in which one object, entity, or substance is changed into another, defying natural expectations and physical laws. The phenomenon of transformation is central to the lexicon of conjuring, relying on methods such as sleight of hand, mechanical apparatus, optical illusions, and misdirection to achieve visual metamorphosis. Transformation is distinguished by its emphasis on the apparent alteration of identity, form, or state, executed in full view of the audience.

Classic examples of transformation include the metamorphosis of a yellow handkerchief into a red handkerchief, the magical transformation of a silk scarf into a dove, a flowerless tree transformed into a tree filled with leaves and oranges (as performed on stage by Robert-Houdin), the change of a playing card into another (called a Color Change, regardless of the card color), or the transfiguration of water into wine. Transformation effects are integral to both close-up and stage magic, a foundation for routines that evoke surprise and wonder. The mechanics of transformation may involve hidden compartments, or sophisticated gimmicks, but the artistic presentation is designed to mask the method and amplify the impossibility of the transformation effect.