The Colt Single Action Army (also known as the SAA, Model P, Peacemaker, or M1873) is a single-action revolver handgun. It was designed for the U.S. government service revolver trials of 1872 by Colt's Patent Firearms Manufacturing Company (today known as Colt's Manufacturing Company) and was adopted as the standard-issued revolver of the U.S. Army from 1873 to 1892.

The Colt SAA has been offered in over 30 different calibers and various barrel lengths. Its overall appearance has remained consistent since 1873. Colt has cancelled its production twice, but renewed it due to popular demand. The revolver was dubbed the "Peacemaker", and is a famous piece of Americana and the American Wild West era, due to its popularity with ranchers, lawmen, and outlaws alike. Today, it is mainly bought as memorabilia by collectors and re-enactors. Its design has influenced the production of numerous other models from other companies.

The original length of the barrel, issued to the U.S. Cavalry, was 7+1⁄2 inches (19 cm), with an overall length of 13 inches (33 cm).

Bound by the Rollin White patent (#12,648, April 3, 1855), and not wanting to pay a royalty fee to Smith & Wesson, Colt could not begin development of bored-through revolver cylinders for metallic cartridge use until April 4, 1869. For the design, Colt turned to two of its best engineers: William Mason and Charles Brinckerhoff Richards who had developed a number of revolvers and black powder conversions for the company. Their effort was designed for the United States government service revolver trials of 1872 by Colt's Patent Firearms Manufacturing Company and adopted as the standard military service revolver. Production began in 1873 with the Single Action Army model 1873, also referred to as the "New Model Army Metallic Cartridge Revolving Pistol".

The first production Single Action Army, serial number 1, thought lost for many years after its production, was found in a barn in Nashua, New Hampshire, in the early 1900s. This gun was chambered in .44 S&W, a centerfire design containing charges of up to 40 grains (2.6 g) of fine-grained black powder and a 255-grain (16.5 g) blunt roundnosed bullet. Relative to period cartridges and most later handgun rounds, it was quite powerful in its full loading.

The Colt Single Action Army revolver, along with the 1870 and 1875 Smith & Wesson American and Model 3 "Schofield" revolvers, replaced the Colt 1860 Army Percussion revolver. The Colt quickly gained favor over the S&W and remained the primary U.S. military sidearm until 1892 when it was replaced by the .38 Long Colt caliber Colt Model 1892, a double-action revolver with swing-out cylinder. By the end of 1874, serial no. 16,000 was reached; 12,500 Colt Single Action Army revolvers chambered for the .45 Colt cartridge had entered service and the remaining revolvers were sold in the civilian market.

The Single Action Army became available in standard barrel lengths of 4+3⁄4 inch, 5+1⁄2 inch, as well as the Cavalry standard, original 7+1⁄2 inch. The shorter barrelled revolvers are sometimes called the "Civilian" or "Gunfighter" model (4+3⁄4 inch) and the Artillery Model (5+1⁄2 inch). There was also a variant with a sub-4-inch barrel, without an ejector rod, unofficially called the "Sheriff's Model", "Banker's Special", or "Storekeeper".

From 1875 until 1880 Colt marketed a single-action revolver chambered in .44 Henry in a separate number range from no. 1 to 1,863.