The Dust Bowl, or the Dirty Thirties, was a period of severe dust storms causing major ecological and agricultural damage to American and Canadian prairie lands in the 1930s. The phenomenon was caused by severe drought combined with a failure to apply dryland farming methods to prevent wind erosion. Extensive deep plowing of the virgin topsoil of the Great Plains in the preceding decade had displaced the natural deep-rooted grasses that normally kept the soil in place and trapped moisture even during periods of drought and high winds. Rapid mechanization of farm implements, especially small gasoline tractors and widespread use of the combine harvester, were significant in the decisions to convert arid grassland (much of which received no more than 10 in of precipitation per year) to cultivated cropland.

During the drought of the 1930s, without natural anchors to keep the soil in place, it dried, turned to dust, and blew away with the prevailing winds. At times, the clouds blackened the sky, reaching all the way to East Coast cities such as New York City and Washington, D.C.. These immense dust storms – given names such as "black blizzards" and "black rollers" – often reduced visibility to a few feet (a meter) or less. The "Black Sunday" black blizzards of April 14, 1935, were witnessed by Associated Press reporter Robert E. Geiger who happened to be in Boise City, Oklahoma that day; the term Dust Bowl was coined by Edward Stanley, Kansas City news editor of the Associated Press, while rewriting Geiger's news story.

The drought and erosion of the Dust Bowl affected 100000000 acre, centered on the panhandles of Texas and Oklahoma, and adjacent sections of New Mexico, Colorado, and Kansas.

Hundreds of thousands of people were forced to leave their farms; many of these families (often known as "Okies", since so many came from Oklahoma) migrated to California and other states, where they found economic conditions little better than those they had left, because of the Great Depression. Author John Steinbeck wrote The Grapes of Wrath and Of Mice and Men about such people.