Carcinisation (or carcinization) is a hypothesised process whereby a crustacean evolves into a crab-like form from a non-crab-like form. The term was introduced by L. A. Borradaile, who described it as "one of the many attempts of Nature to evolve a crab".

Carcinisation is believed to have occurred in at least five groups of decapod crustaceans, independently, most notably king crabs which most scientists believe evolved from hermit crab ancestors (there is still some debate over this point). The other examples are the family Porcellanidae, or porcelain crabs; these are closely related to squat lobsters, Lomis, Birgus latro, and the Brachyura itself (true crabs)