A foam is a substance that is formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas.

Foam may refer to:

• Foam, a substance that is formed by trapping gas bubbles in a liquid or solid.
• Foam (culinary), a modern food preparation and presentation technique
• Foam (organization), also FoAM, an arts and technology organization
• Foam hand, a sports paraphernalia item
• FOAM, a photography museum located in Amsterdam
• OpenFOAM, an open source finite volume pde solver used in a variety of computational fluid dynamics applications
• USS Foam (ID-2496), a United States Navy trawler and minesweeper in commission from 1918 to 1919
• First Office Action on the Merits, a form of Office action in U.S. patent law