Siege of Atlanta, campaign during the American Civil War (1861-1865) in which the Union Army sought to capture the principal Confederate railroad and supply center in Atlanta, Georgia. The siege lasted from July 20 to September 2, 1864. It had a major influence on the outcome of the war and on the presidential election in the fall of 1864.

On July 17 General William Sherman and 100,000 of his Union soldiers advanced southward from Dalton, Georgia. They crossed the Chattahoochee River and took positions north of Atlanta. Confederate general John B. Hood, in command of the 50,000 troops that had thus far resisted Sherman's advance, attacked the Union troops on July 20. Hood was beaten off with a loss of some 5,000 men. Two days later, he pitted his battle-tired men, who had marched 24 km (15 mi) the night before, against Union general James B. McPherson's army to the east of the city. This engagement, known as the Battle of Atlanta, ended in a draw.

On July 28 the Confederates again attacked the Union soldiers, but the Southerners were repulsed. This battle—the Battle of Ezra Church—took place a short distance to the west of the city. From July 20 until late August, Sherman besieged Atlanta, shelling it from the north and west and seeking to reach the city’s two essential railroads to the south. After winning the Battle of Jonesboro just south of Atlanta on September 1, Sherman succeeded in reaching the railroads. The following morning Atlanta was surrendered. The Union victory proved essential in furthering the cause of President Abraham Lincoln and in aiding in his reelection.