The Carl Gustaf 84 mm recoilless rifle (Swedish pronunciation: [kɑːɭ ˈɡɵ̂sːtav], named after Carl Gustafs Stads Gevärsfaktori, which initially produced it) is a Swedish-developed 84 mm (3.3 in) caliber shoulder-fired recoilless rifle, initially developed by the Royal Swedish Army Materiel Administration during the second half of the 1940s as a crew-served man-portable infantry support gun for close-range multi-role anti-armour, anti-personnel, battlefield illumination, smoke screening and marking fire, which has seen great export success around the globe and continues to be a popular multi-purpose support weapon in use by many nations. The Carl Gustaf 84 mm recoilless rifle is a lightweight, low-cost weapon that uses a wide range of ammunition, which makes it extremely flexible and suitable for a wide variety of roles.

Development of the initial model started from 1946 as one of the many recoilless rifle designs of that era, based on the experience from the earlier Carl Gustaf 20 mm recoilless rifle and the success of man-portable rocket launchers during World War II, such as the bazooka and Panzerschreck. Production of the initial model was handled by Carl Gustafs Stads Gevärsfaktori led by Försvarets Fabriksverk (FFV) and the weapon received the designation 8,4 cm granatgevär m/48, (8,4 cm grg m/48 – "8,4 cm grenade rifle", model 1948) in Swedish service. FFV would continue to further develop the weapon for the international market, later being merged into Saab Bofors Dynamics which handles development and export today. While similar weapons have generally disappeared from service, the Carl Gustaf is still in production and remains in widespread use.

The weapon goes under many names around the globe. It is most frequently called the "Carl Gustaf" or similar for short. British troops, for example, refer to it as the "Charlie G", while Canadian troops often refer to it as "Carl G". In Australia, it is irreverently known as "Charlie Gutsache" (guts ache, meaning stomach pain), or "Charlie Swede".

In US military service, it is officially known as the M3 Multi-Role Anti-Armor Anti-Personnel Weapon System (MAAWS) or Ranger Antitank Weapons System (RAWS), but is often simply called the "M3 Carl Gustaf" or just "Gustaf".

In Swedish military service, it is officially known as the 8,4 cm granatgevär m/48, m/86 and m/18, depending on the model (M1, M3, M4), but is often simply referred to as the "GRG" (gé-er-gé) after their type designation abbreviation (from granatgevär, meaning "grenade rifle"), since all models fire the same general ammunition and are used in much the same way (although the 84 mm grg m/18 can use programmable and guided ammunition).

The basic weapon consists of the main tube with the breech-mounted Venturi recoil damper, with two grips near the front and a shoulder mount. The weapon is fitted with iron sights, but is normally aimed with the attached 3× optical sight with a 17 degree (300 mil) field of view. The most modern variants fielded by Swedish rifle companies have been fitted with the Swedish Aimpoint sighting system. Luminous front and rear sight inserts are available for the iron sights when aiming at night, and an image intensification system may also be used.

The Gustaf can be fired from the standing, kneeling, sitting or prone positions, and a bipod may be attached in front of the shoulder piece. An operating handle called the "Venturi lock" is used to move the hinged breech to one side for reloading.

The weapon is normally operated by a two-man crew, a gunner who carries and fires the weapon and a loader, carrying two canisters for a total of four rounds of ammunition. One or two extra ammunition carriers can be assigned if heavy use is expected. In the firing procedure it is the loader's responsibility to check the area behind the weapon for people and for obstacles that can interfere with the back-blast; this is needed due to the inherent dangers of the back-blast. Any person within the back-blast cone can suffer severe burn injuries and solid objects closely behind can reflect the blast back onto the crew.