Black Monday, October 28, 1929, saw the largest percentage drop in the Dow Jones Industrial Average before Black Tuesday.
The Dow fell 38.33 points, or 12.82%, on Black Monday as selling intensified during the Wall Street Crash. The decline followed Black Thursday on October 24 and preceded the even larger-volume panic of Black Tuesday on October 29.
The crash reflected a combination of highly valued stocks, widespread margin buying, tightening credit, and weakening economic conditions. Investors who had borrowed to buy shares faced margin calls, forcing additional selling as prices fell.
Black Monday in 1929 should not be confused with Black Monday on October 19, 1987. The 1987 event produced the Dow's largest one-day percentage decline in its history, while the 1929 date was part of the crash that preceded the Great Depression. The same nickname is therefore used for two different historic market collapses.