Some goods are consumed not just for their intrinsic utility but also for the impression their consumption has on others. We analyze the market for such a commodity—diamonds. We collect data on price and other attributes from the inventories of three large online retailers of diamonds. We find that people are willing to pay premiums upward of 18% for a diamond that is one-half carat rather than slightly less than a half carat and between 5% and 10% for a one-carat rather than a slightly less than one-carat stone. Since a major portion of larger gem-quality diamonds are used for engagement rings, such an outcome is consistent with Bernheim's model of conformism, where individuals try to conform to a single standard of behavior that is often established at a focal point. In this case, prospective grooms signal their desirability as a mate by the size of the diamond engagement ring they give their fiancées.