The Vickers machine gun or Vickers gun is a name primarily used to refer to the water-cooled .303 inch (7.7 mm) machine gun produced by Vickers Limited, originally for the British Army. The machine gun typically required a six to eight-man team to operate: one to fire, one to feed the ammunition, the rest to help carry the weapon, its ammunition and spare parts. It served from before the First World War until the 1960s.

The weapon had a reputation for great solidity and reliability. Ian V. Hogg, in Weapons & War Machines, describes an action that took place in August 1916, during which the British Army's 100th Company of the Machine Gun Corps fired their ten Vickers guns continuously for twelve hours. Using 100 new barrels, they fired a million rounds without a single breakdown. "It was this absolute foolproof reliability which endeared the Vickers to every British soldier who ever fired one."

The Vickers machine gun was based on the successful Maxim gun of the late 19th century. After purchasing the Maxim company outright in 1896, Vickers took the design of the Maxim gun and improved it, reducing its weight by lightening and simplifying the action and substituting components made with high strength alloys. A muzzle booster was also added.

A machine gun is a fully automatic mounted or portable firearm, usually designed to fire rounds in quick succession from an ammunition belt or large-capacity magazine, typically at a rate of several hundred rounds per minute.

Machine guns are generally categorized as submachine guns, machine guns, or autocannons. Submachine guns are designed to be small, portable automatic weapons for personal defense or short range combat, and are intended to be fired while being hand held. Submachine guns use small pistol caliber rounds. A proper machine gun is often portable to a certain degree, but is generally used when mounted on a stand or fired from the ground on a bipod. Light machine guns are small enough to be fired and hand held like a rifle, but the gun is more effective when fired from a prone position. The difference between machine guns and autocannons is based on caliber, with autocannons using calibers larger than 16 mm.

Another factor is whether the gun fires conventional rounds or explosive rounds. Guns firing large-caliber explosive rounds are generally considered either autocannons or automatic grenade launchers ("grenade machine guns"). By contrast with the other two categories (sub-machine guns and autocannons), machine guns (like rifles) tend to share the characteristic of a very high ratio of barrel length to caliber (a long barrel for a small caliber); indeed, a true machine gun is essentially a fully automatic rifle, and the boundaries between the two are often blurred. Often, the criterion for a machine gun as opposed to an automatic rifle is considered to be the presence of a quick change barrel or other cooling system (see below).