The Remington 870 was the fourth major design in a series of Remington pump shotguns. John Pedersen designed the fragile Remington Model 10 (and later the improved Remington Model 29). John Browning designed the Remington Model 17 (which was later adapted by Ithaca into the Ithaca 37), which served as the basis for the Remington 31. The Model 31 was well-liked but struggled for sales in the shadow of the Winchester Model 12. To achieve better sales, Remington produced the Model 870 in 1950, which was more modern and reliable in its construction, and relatively inexpensive.

The 870 was a commercial success. They reached two million guns by 1973 (ten times the number of Model 31 shotguns it replaced). As of 1983, the 870 held the record for the best-selling shotgun in history, with three million sold. By 1996, spurred by sales of the basic "Express" models, which were added as a lower-cost alternative to the original Wingmaster line, sales topped seven million guns. On April 13, 2009, the ten-millionth Model 870 was produced.

The 870 features a bottom-loading, side ejecting receiver, and a tubular magazine under the barrel. The gun comes with a plug for migratory bird hunting which reduces the magazine's capacity to two[6] rounds. It has dual action bars, an internal hammer, and a bolt that locks into an extension in the barrel. The action, receiver, fire control group, safety catch, and slide release catch of the Remington Model 870 shotgun are similar to those used on the Remington Model 7600 series pump-action centerfire rifles and carbines. The basic fire control group design was first used in the automatic 11–48. Twelve gauge stocks will also interchange on the older 12-gauge-sized 20-gauge receivers, although modification is needed to fit the smaller sized 20-gauge receivers employed since the late 1970s. Several parts of the 870 will interchange with the semi-automatic Remington 1100 and 11–87.

The original 870 models were offered with fixed chokes. In 1986 Remington introduced the new Remington "Rem Choke" system of screw-in chokes (also fitted to Remington model 1100 auto-loading shotguns at the same time). Initially, the Rem Chokes were offered only in 12 gauge in barrel lengths of 21", 26", and 28". The following year the availability was expanded to the 20 gauge and included other barrel lengths.

Production 870s for over 30 years had a design whereby a user could fail to press a shell all the way into the magazine when loading such that the shell latch did not engage the shell, and such actions could tie up the gun. This was caused by the shell which slipped out of the magazine under the bolt in the receiver to bind the action, requiring rough treatment of the action or even disassembly to clear by the uninitiated. The potential issue was resolved with the introduction of the "Flexi Tab" carrier. Guns with this modification can be identified by the "U"-shaped cut-out on the carrier, visible from below the gun. The cut-out, combined with modified machining on the underside of the slide assembly, allows the action to be opened with a shell on the carrier.

VARIANTS

There are hundreds of variations of the Remington 870 in 12, 16, 20, 28 gauges and .410 bore. In 1969 Remington introduced 28 gauge and .410 bore models on a new scaled-down receiver size, and in 1972 a 20 gauge Lightweight ("LW") version was introduced on the same sized receiver, and all of the smaller gauges today are produced on that size receiver. From the original fifteen models offered, Remington currently produces dozens of models for civilian, law enforcement, and military sales. 870 variants can be grouped into:

Express – Matte blue/black bead-blasted with hardwood, laminated hardwood or synthetic stocks and chambered for 2 3/4" and 3" 12 or 20 gauge shotshells. All Expresses have been chambered in 3" in 12 and 20 gauge, but markings have varied.

Express Tactical – Matte blue/black bead-blasted with a synthetic stock and chambered for 2 3/4" and 3" 12 gauge shotshells. The Express Tactical (stamped "Remington 870 Tactical") has an 18.5 inches (470 mm) barrel and is offered with 4+1 or 6+1 magazine tube capacities.

Mark 1 – adopted by the United States Marine Corps in the late 1960s and saw service into the 21st century. The Model 870 Mark 1 has a 21-inch (53 cm) barrel with an extended magazine increasing total capacity to 8 rounds, and was fitted with an adapter allowing the use of the standard M7 bayonet for the M16 rifle.

MCS (Modular Combat Shotgun) – A new modular variant of the Model 870 which can be quickly modified with different barrels, magazine tubes, and stocks for different purposes, such as urban combat and door breaching.

Police Magnum – The law enforcement version of the Model 870, the Police Magnum, is chambered in 12 gauge 3" magnum. It can be ordered with two options: a blued or Parkerized steel finish. These models feature a sturdier sear spring, carrier latch spring, and a forged steel extractor (as opposed to the metal injection molded extractor used on the 870 Express variants). The receivers are stamped with the insignia "Remington 870 Police Magnum" beginning 2014. They are equipped with Police Magnum-specific walnut hardwood or polymer stocks which are fitted with sling mounts. The walnut stocks omit the checkering that is present on the Express/Wingmaster variants. 870 Police Magnum models come with matching walnut or polymer pumps that are decreased in length to prevent interference with most vehicle-mounted rack systems. The shortened pump also allows quick visual inspection of the internal magazine regardless of what position the pump is in, whereas the optional lengthened sport-type pump on other models partially blocks the loading port when it is pulled to the rear position. Police Magnum models are available with 18" or 20" barrels, with or without iron rifle sights, and have a standard magazine tube capacity of four rounds. They can be ordered with a two or three-round extended magazine tube from the factory, bringing total capacity to 7 (+1) shotshells (18" barrel) or 8 (+1) shotshells (20" barrel). All Police Magnum barrels come with an improved cylinder choke unless specially ordered to fit the user's needs.

Special Purpose Marine Magnum – Corrosion-resistant nickel-plating covering all internal and external metal parts with black synthetic furniture.

Special Purpose Waterfowl - Matte, Parkerized finish on barrel and receiver, satin-finished American walnut stock and forearm with cut(not pressed)checkering, sling swivels, a camo sling were standard. It was a 3" gun. This model is sometimes confused with the Express, but it was more closely related to the Wingmaster line, with a commensurate price tag.

Super Mag – Chambered for 3½" 12 gauge shotshells and has a spring-loaded dust cover on the bolt to allow for a larger opening while keeping the receiver the same length.

Wingmaster – Blued steel with high gloss or satin walnut stocks. They have been offered in Skeet, Trap, and field configurations. Originally the basic Wingmaster was chambered for 2 3/4" rounds and came with a fixed choke, and the 3" chambered versions were designated Magnum models. Models built after 1986 offer the RemChoke Interchangeable choke tube system, and the 12 and 20 gauge versions are chambered in 3" for either 2 3/4" or 3" shells. Prior to the introduction of the "Police Magnum" model 870, altered Wingmasters were popular among law enforcement.

Tac-14 – Black oxide receiver finish, with a synthetic stock. The Tac-14 is extremely compact by design, but retains the reliability and stopping power of previous models. It is chambered in 12 gauge, with a 14" barrel and a capacity of 4+1. Due to its unique design, the Tac-14 is not designated a shotgun, but a firearm. Since it comes from the factory without a stock, and its overall length being over 26", it is not considered an NFA AOW (National Firearms Act Any Other Weapon).[12] It is marketed and sold with a black synthetic Raptor "pistol grip" and Magpul M-LOK forend.

Tac-14 DM - Tac-14, featuring an external box magazine rather than the internal tube magazine in other models. This allows for the size of the Tac-14, but a capacity of 6+1.

Tac-14 Marine Magnum - Identical form and function as the standard Tac-14 but with the same nickel plating on all metal parts as the Special Purpose Marine Magnum.

870 DM - Matte Blue receiver finish with a synthetic stock. Differs from other 870 models with an external box magazine, similarly to the Tac-14 DM, allowing a capacity of 6+1.

200th Anniversary Edition – To celebrate the 200th Anniversary of Remington, two models were designed. One was a Wingmaster with some styling in the wood and a golden emblem on the bottom of the stock. The second was a limited edition Wingmaster that stopped production after 2016, with the same styling, but extended across the entirety of the stock and pump, and also extends to the receiver and barrel, with a golden ring on the end of the barrel. The emblem on the bottom is also a richer gold, possibly real gold, and there is a golden ribbon under the shell ejection reading "1816 Bicentennial 2016" along with a golden trigger, and a golden symbol of a hunter with a firearm in hand walking.

Wilson Arms Executive Protection - Ultra short model. Sawed-off barrel, with pistol grip and vertical fore grip.