Battle of Chattanooga, major engagement of the American Civil War, fought on November 23-25, 1863, between a Union army of about 60,000 men under General Ulysses S. Grant and a Confederate force of approximately 40,000 under General Braxton Bragg. Following an earlier defeat at Chickamauga, in northwest Georgia, the Union army withdrew across the state line to Chattanooga, Tennessee. The Confederates laid siege and cut off Union supply lines and communications. Bragg's army was entrenched on Lookout Mountain, 5 km (3 mi) southwest of Chattanooga, and on parts of Missionary Ridge, running parallel to Lookout Mountain.

On October 27-28 Union forces seized Brown's Ferry on the Tennessee River, west of Chattanooga, restoring a supply route into the city. Troops of the XI and XII Corps, under the Union general Joseph Hooker, also seized the valley of Lookout Creek, west of Lookout Mountain. Grant then halted further operations until the arrival of four reinforcement divisions under General William Tecumseh Sherman. On November 23 Union troops captured Orchard Knob, an elevation in the plain between Chattanooga and Missionary Ridge. Grant ordered an assault on Lookout Mountain at 8 am on November 24, and by the morning of November 25 Hooker had driven the Confederates from their positions.

The decisive phase of the battle began at 7 am on November 25, when Sherman's force, consisting of six divisions, attacked Confederate entrenchments on the northern slopes of Missionary Ridge. Unable to make headway, however, Grant ordered General George Thomas to make a diversionary assault on the Confederate earthworks along the western base of the ridge. Simultaneously, Hooker's forces stormed the southern and eastern flanks of Missionary Ridge. Thomas's men, disregarding orders to advance no farther than the first line of earthworks, continued on up the steep slopes and, in one of the most remarkable charges in military history, carried the enemy fortifications along the crest. The panic-stricken Confederate troops fled in disorder. During the night the remnants of Bragg's army withdrew northward.

Grant's victory forced the Confederates to evacuate Tennessee and made possible Sherman's subsequent march through Georgia. Union casualties in the battle were about 5800; Confederate casualties, about 6700. The battlefield was established as the Chickamauga and Chattanooga National Military Park in 1890.