Hard support structure found on an organism's outside rather than inside of a body.

Exoskeletons form the support skeletons of as well as most mollusks. See also and . Basically, if it is hard (that is, rather than more ), supports an organism's body, and otherwise is found on the outside rather than the inside of that body, then it is an exoskeleton.

In addition to playing roles in the support of , hard, external coverings also play roles in the production of animals such as from . In addition, the fossil record specially of organisms is with exoskeltons of various sorts.