The Bradley-Martin Ball was a lavish costume ball at the Waldorf Hotel in New York City on the night of February 10, 1897. Cornelia Bradley-Martin, wife of Bradley Martin, organized the ball. Eight hundred socialites spent about $400,000 imitating kings and queens. Bradley-Martin's stated intention was to create an economic stimulus for New York City, which was at the end of the Long Depression which began in 1873 and included the Panic of 1893. The Bradley-Martins spent approximately $9.7 million in today's money to throw the ball. Across the country, preachers and editorial writers argued over the propriety of a party that would cost hundreds of thousands of dollars. In the end, the ball was a social triumph but created negative publicity.

A costume party or fancy dress party is a type of party, common in contemporary Western culture, in which many of the guests are dressed in costume, usually depicting a fictional or stock character, or historical figure. Such parties are popular in the United States, United Kingdom, Canada, Australia, Ireland and New Zealand, especially during Halloween.