A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have decomposed or been eaten by another animal.

Beachcombing is an activity that consists of an individual "combing" the beach and the intertidal zone, looking for things of value, interest or utility. A beachcomber is a person who participates in the activity of beachcombing.