By modern convention, the ring is usually presented by a man to his prospective bride while or directly after she accepts his marriage proposal.
Such a tradition seems to date at least to the ancient Greeks and Romans.
Designs of such rings have varied greatly over the years. Current fashions for engagement rings are for a gold or silver band with a single diamond. This trend dates from advertising campaigns in the 1940s by de Beers, the world's near-monopoly diamond producer.