Sea glass is a type of glass that is naturally weathered by the physical and chemical processes of saltwater bodies, such as oceans and seas. It is formed from discarded glass objects, such as bottles, jars, and tableware, that are broken and then tumbled smooth by the waves and currents over many years. The weathering processes produce natural frosted glass, and the resulting sea glass often has the appearance of tumbled stones. Sea glass takes 20-40 years, and sometimes as much as 100-200 years, to acquire its characteristic texture and shape. It is also colloquially referred to as drift glass from the longshore drift process that forms the smooth edges. Sea glass is used for decoration, most commonly in jewelry.

Sea glass is sometimes used interchangeably with the term "beach glass," but the two are actually different, despite being quite similar superficially. Unlike sea glass, which comes from saline water of the seas, beach glass comes from freshwater sources, and typically has a less frosted appearance and a different pH balance than real sea glass. However, in most practical situations, these terms can be used interchangeably.

Sea glass is a valuable commodity, especially if it is genuine and beach-found. Rare sea glass colors, including turquoise, orange, or red, have even more value than the more common colors of greens, whites, and browns. Sea glass is now used to create fashionable necklaces, earrings, bracelets, and mosaic-type art. It is trendy, in demand, and its supply is diminishing.