The best-known sources of pearls are marine mollusks, especially the pearl oysters, conchs and abalone found worldwide. Each species has a unique form, ecology and history.

Mollusks first evolved 530 million years ago, and fossil pearls have been found in several extinct species. Some of the most unusual natural pearls today—pink conch pearls from the Queen Conch, blue-green pearls from abalone and orange melo pearls from Baler Shells—are produced by marine snails. Humans have long harvested these and other marine mollusks for their mother-of-pearl shells and natural pearls. Today many species of mollusks are raised in pearl culturing, also called "perliculture," producing cultured pearls in a wide range of shapes, sizes and colors.