The American Civil War saw extensive use of horse-mounted soldiers on both sides of the conflict. They were vital to both the Union Army and Confederate Army for conducting reconnaissance missions to locate the enemy and determine their strength and movement, and for screening friendly units from being discovered by the enemy's reconnaissance efforts. Other missions carried out by cavalry included raiding behind enemy lines, escorting senior officers, and carrying messages.

In the first half of the war, the Confederates enjoyed the advantage in cavalry, not least because most of the experienced cavalry officers from the Regular Army had chosen to side with the Confederacy. Notable Confederate cavalry leaders included J. E. B. Stuart, famed for literally riding rings around the Union's Army of the Potomac, and Nathan Bedford Forrest, who caused havoc with Union supply lines.

The Battle of Brandy Station in 1863 is considered the point by which Union cavalry proved itself equal to the Confederates, and onward through the second half of the war they continued to improve. This was exemplified by Benjamin Grierson's brilliant deception tactics in the Mississippi valley, and Philip Sheridan's aggressive movements while in command of the Army of the Shenandoah at the end of the war in Virginia.

Cavalry units proved highly expensive to maintain, and unscrupulous agents would often exploit shortages by supplying defective animals at exorbitant prices. The Union benefited from the creation of tighter regulations and a centralized acquisition and distribution system which ensured its forces remained mounted throughout the war. Conversely, the Confederacy's system of each soldier supplying their own horses resulted in the degradation of its cavalry units as horses became harder to obtain.

There were a variety of mounted forces prevalent in the Civil War, although for the sake of brevity they are often referred to under the catchall term "cavalry". Some units named themselves after European cavalry such as hussars and lancers, but these names were considered obsolete and used out of tradition rather than as an accurate description. Approximately fourteen percent of the Union Army consisted of cavalry, while in the Confederate States Army about twenty percent of soldiers were mounted.

At the time of the American Civil War, the cavalry had six major roles to play:

Of these missions, reconnaissance was the most important role. Their inherent nature made cavalry ideally suited to be the "eyes and ears" of an army's commander and keep him informed of the enemy's position and movements. Cavalry had the agility and firepower to probe the enemy for weak points, set ambushes for isolated groups, and flee before the main force could overwhelm them. The widespread availability of field glasses only increased their information-gathering capabilities.

Reconnaissance and screening were crucial components in the Gettysburg Campaign, where cavalry under Union General Alfred Pleasonton attempted to find the wide-ranging Army of Northern Virginia on its invasion of the North, and Confederate cavalry under J.E.B. Stuart effectively employed counter-reconnaissance to screen passes in the Blue Ridge Mountains and hide Robert E. Lee's movements from the Army of the Potomac. However, when Stuart was "cut loose" to conduct another raid around the Army of the Potomac, he deprived Lee of adequate reconnaissance at the beginning of the Battle of Gettysburg, one of the principal reasons for the Confederate defeat there.