Forty acres and a mule was part of Special Field Orders No. 15, a wartime order proclaimed by Union General William Tecumseh Sherman on January 16, 1865, during the American Civil War, to allot land to some freed families, in plots of land no larger than 40 acres (16 ha). Sherman later ordered the army to lend mules for the agrarian reform effort. The field orders followed a series of conversations between Secretary of War Edwin M. Stanton and Radical Republican abolitionists Charles Sumner and Thaddeus Stevens following disruptions to the institution of slavery provoked by the American Civil War. Many freed people believed, after being told by various political figures, that they had a right to own the land they had been forced to work as slaves and were eager to control their own property. Freed people widely expected to legally claim 40 acres of land. However, Abraham Lincoln's successor as president, Andrew Johnson, tried to reverse the intent of Sherman's wartime Order No. 15 and similar provisions included in the second Freedmen's Bureau bills.

Special Field Orders, No. 15 were military orders issued during the American Civil War, on January 16, 1865, by General William Tecumseh Sherman, commander of the Military Division of the Mississippi of the United States Army. They provided for the confiscation of 400,000 acres (160,000 ha) of land along the Atlantic coast of South Carolina, Georgia, and Florida and the dividing of it into parcels of not more than 40 acres (16 ha), on which were to be settled approximately 18,000 formerly enslaved families and other black people then living in the area.