Provided are a film in which the balance between hydrophilicity and abrasion resistance is superior, decrease in hydrophilicity by water is minimal, and the weather resistance is also superior; as well as a polymer and a polymer composition that can yield such a film. The film of the invention is prepared from a specific copolymer (i) having a sulfonic acid-containing group, an epoxy group, and a specific alkoxysilyl group in a molecule, or from a composition including the copolymer (i).