Molting, or Moulting, the shedding, or casting off, of feathers, hair, horns, shell, or a layer of skin by an animal. Molting is a periodic process of renewal, the cast-off parts being replaced by a new growth. For example, an insect's shell-like skin does not stretch, but splits and falls away as the body grows. There are usually several molts before an insect reaches the adult stage. A lobster or other crustacean usually molts its exoskeleton (hard protective covering) in the spring or early summer. The animal is quite weak and helpless for a time, for the new skin lacks the calcium that gave hardness to the old.

An amphibian, such as a frog or toad, molts its skin every few weeks except in winter. Some amphibians eat their shed skin. The pelage, or hairy covering, of most mammals is shed in the fall so that a heavier winter coat can be grown. Deer have two molts, one in the fall and one in the spring. Deer shed their antlers and grow larger ones each year. Birds usually molt once a year, but some species shed their plumage two or three times a year.