Britannia silver is an alloy of silver containing 95.84% silver, with the balance usually copper.

This standard was introduced in England by Act of Parliament in 1697 to replace sterling silver (92.5% silver) as the obligatory standard for items of "wrought plate". The lion passant gardant hallmark denoting sterling was replaced with "the figure of a woman commonly called Britannia", and the leopard's head mark of the Worshipful Company of Goldsmiths replaced with a "lion's head erased".

Britannia standard silver was introduced by the English government as part of the great recoinage scheme of William III from 1696, when attempts were made to limit the clipping and melting of sterling silver coinage. It was thought that by maintaining a higher standard for plate, there would be less incentive to put the newly issued sterling coins in the melting pot.

Sterling silver was approved again for use by silversmiths from 1 June 1720, and thereafter Britannia silver has remained an optional standard for silver assay in the United Kingdom and Ireland. Since the hallmarking changes of 1 January 1999, Britannia silver has been denoted by the millesimal fineness hallmark 958, with the symbol of Britannia being applied optionally.