A seashell or sea shell, also known simply as a shell, is a naturally occurring, hard, protective outer layer created by an animal that lives in the sea. If you've ever walked on a beach, you've seen seashells, and maybe even collected some to take home. Most shells that are found on beaches are usually made of calcium carbonate. Most seashells come from molluscs, a large group of marine animals including clams, mussels, and oysters, which exude shells as a protective covering.  These shells, because of their bright colours, rich variety of shapes and designs, and abundance along seashores, have long been used for ornaments, tools, and coins. Seashells are commonly found in beach drift, which are natural deposits found along strandlines on beaches by the waves and the tides.

Seashells have been used as a medium of exchange and currency in various places, including many Indian Ocean and Pacific Ocean islands, also in North America, Africa and the Caribbean. Seashells have often been used as tools, because of their strength and the variety of their shapes. Seashells have been used as musical instruments, wind instruments for many hundreds if not thousands of years. Whole seashells or parts of sea shells have been used as jewelry or in other forms of adornment since prehistoric times. Shells historically have been and still are made into, or incorporated into, necklaces, pendants, buttons, beads, earrings, brooches, rings, belt buckles and other uses. Small pieces of coloured and iridescent shell have been used to create mosaics and inlays, which have been used to decorate walls, furniture and boxes. Large numbers of whole seashells, arranged to form patterns, have been used to decorate mirror frames and furniture.