During the 1929 Wall Street Crash, Black Monday was October 28, 1929, when the Dow Jones Industrial Average fell nearly 13%.
The decline followed a sharp loss of confidence after weeks of market weakness. Heavy selling overwhelmed the New York Stock Exchange, and the Dow dropped 38.33 points, or about 12.8%, in one session.
Black Tuesday followed on October 29 and brought an even larger trading volume and a further fall of about 12%. The two dates are often discussed together because they intensified the crash and helped turn a market collapse into a wider financial crisis.
The crash did not single-handedly cause the Great Depression, but it damaged banks, businesses, investors, and public confidence. A common mix-up is calling October 24 Black Monday; that earlier date is usually known as Black Thursday.