The Bren gun (Brno-Enfield) was a series of light machine guns (LMG) made by the United Kingdom in the 1930s and used in various roles until 1992. While best known for its role as the British and British Empire forces' primary infantry LMG in World War II, it was also used in the Korean War and saw service throughout the latter half of the 20th century, including the 1982 Falklands War. Although fitted with a bipod, it could also be mounted on a tripod or be vehicle-mounted.

The Bren gun was a licensed version of the Czechoslovak ZGB 33 light machine gun which, in turn, was a modified version of the ZB vz. 26, which British Army officials had tested during a firearms service competition in the 1930s. The designer was Václav Holek, a gun inventor and design engineer. The later Bren gun featured a distinctive top-mounted curved box magazine, conical flash hider, and quick change barrel.

In the 1950s, many Bren guns were re-barrelled to accept the 7.62×51mm NATO cartridge and modified to feed from the magazine for the L1 (Commonwealth version of the FN FAL) rifle as the L4 light machine gun. It was replaced in the British Army as the section LMG by the L7 general-purpose machine gun (GPMG), a belt-fed weapon. This was supplemented in the 1980s by the L86 Light Support Weapon firing the 5.56×45mm NATO round, leaving the Bren gun in use only as a pintle mount on some vehicles. The Bren gun was manufactured by Indian Ordnance Factories as the "Gun Machine 7.62mm 1B" before it was discontinued in 2012.

The name Bren was derived from Brno, the city in Czechoslovakia, where the Zb vz. 26 was designed (in the Zbrojovka Brno Factory) and Enfield, site of the British Royal Small Arms Factory.

At the close of World War I in 1918, the British Army was equipped with two main automatic weapons; the Vickers medium machine gun (MMG) and the Lewis light machine gun. The Vickers was heavy and required a supply of water to keep it in operation, which tended to relegate it to static defence and indirect fire support. The Lewis, although lighter, was still heavy and was prone to frequent stoppages: its barrel could not be changed in the field, which meant that sustained firing resulted in overheating until it stopped altogether.

In 1922, to find a replacement for the Lewis, the Small Arms Committee of the British Army ran competitive trials between the Madsen machine gun, the M1918 Browning Automatic Rifle (BAR), the Hotchkiss M1909 machine gun, the Beardmore–Farquhar rifle, and the Lewis itself. Although the BAR was recommended, the sheer number of Lewis guns available and the difficult financial conditions meant that nothing was done. Various new models of light machine gun were tested as they became available, and in 1930, a further set of extensive trials commenced, overseen by Frederick Hubert Vinden. This time the weapons tested included the SIG Neuhausen KE7, the Vickers–Berthier and the Czechoslovak ZB vz. 27. The last did not meet high requirements for durability and reliability, mainly because gunpowder residue from British cordite was obstructing the gas tube (ZB vz. 27 was also sent in 7.92 Mauser instead of .303 British, but ZB already held a patent for a staggered magazine for rimmed rounds). The Vickers–Berthier was later adopted by the Indian Army because it could be manufactured at once, rather than wait for the British Lewis production run to finish; it too saw extensive service in World War II.

A modified variant with a shortened gas tube was tested again in June 1932, and then newly developed ZB-30 in .303 yet again tested in November. Receiving more feedback and incorporating it into the design by January 1933, yet two other modifications were tested by British representatives in Brno in July. One of the variants was selected, designated ZGB 33 (for Zbrojovka, United Kingdom, 33), and 10 samples were sent to England in autumn 1933. After additional trials in early 1934, more samples were ordered during the summer of 1934, and on May 24, 1935, the licence for British manufacture was finally acquired, and the design was adopted under the Bren name.

The major changes were in the magazine and barrel and the lower pistol grip assembly which went from a swivelling grip frame pivoted on the front of the trigger guard to a sliding grip frame which included the forward tripod mount and sliding ejection port cover. The magazine was curved in order to feed the rimmed .303 inch SAA ("Small Arms Ammunition") cartridge, a change from the various rimless Mauser-design cartridges such as the 7.9-mm Mauser round previously used by Czech designs. These modifications were categorised in various numbered designations, ZB vz. 27, ZB vz. 30, ZB vz. 32, and finally the ZGB 33, which was licensed for manufacture under the Bren name.^{[citation needed]}