Most grenade launchers are man-portable, shoulder-fired weapons, usually mounted on a rifle such as the AK-47 or M16. However, many can be used independently, such as the M79 and AG36. These are almost always single shot, manually reloaded weapons firing 30–40 millimeter caliber grenades which rarely resemble hand grenades, but look more like miniature artillery shells.

  The most standard grenade round today is the 40mm grenade, which has a wide variety of applications in man-portable and vehicle mounted weapons systems. With this standardization, there are many new 'specialty' grenades available, from rounds that can be used as a flare, infared flare, or even a video camera that surveys the battlefield from a bird's eye view.

 There are also heavier examples, including automatic grenade launchers for ground and vehicle use, such as the American Mk 19. Capable of a relatively high rate of fire, these automatic grenade launchers are used for suppressive fire and to destroy or disable light vehicles and buildings. Some armored fighting vehicles also mount grenade launchers as a means of defense, usually firing smoke grenades to conceal the vehicle behind a smoke screen, though can also be loaded with chaff, flares, or anti-personnel grenades to repel infantry attacks.

 The man-portable grenade launcher can either come in the form of a standalone weapon (either single-shot or repeating weapons, the latter resembling a large revolver); or an underbarrel weapon which is permanently mounted to the rifle. Alternatively, many rifles have been designed to fire grenades from their muzzle, using either a special blank propellant cartridge or a central hole through the grenade allowing the bullet to pass through.

 This system has two key advantages: the grenade can generally be made larger and more powerful as compared to underbarrel or standalone weapons, and the rifle's weight and handling characteristics are not affected as with underbarrel systems.

 The disadvantage of this method is that when a soldier wants to launch a grenade he must unload the weapon and then load the propellant cartridge and grenade. If he is surprised by a close-range threat while preparing to fire the grenade, he has to reverse the above procedure and cannot immediately react with rifle fire.

 In underbarrel systems, the rifle portion and launching portion of the weapon can both be carried loaded and ready to fire. Underbarrel tubes generally have their own trigger and use the rifle's magazine as a grip for the firing hand. To fire, one simply changes grips, disengages the safety and pulls the trigger. In most systems the barrel either slides forward or pivots to the side to allow reloading. For aiming, the M203 mounts either a flip-up rear sight, which is notched for different ranges and utilizes the rifle's existing front sight, or a "quadrant" sight which mounts to the side of the carrying handle. Recoil from such weapons is significant, comparable to a high-power shotgun.

 The M79 grenade launcher is a single-shot, shoulder-fired, break open grenade launcher which fires a 40 x46 mm grenade and first appeared during the Vietnam War. Because of its distinctive firing sound, among American soldiers, it earned the nicknames of "Thump-Gun", "Thumper", or "Blooper", but Australian units referred to it as the "Wombat Gun". The M79 resembles a large bore, break-action, sawed-off shotgun, and can fire a wide variety of 40 mm rounds, including explosive, anti-personnel, smoke, buckshot, flechette, and illumination. However, its size and single-shot nature means that a soldier with a M79 would be dedicated to being only a grenadier. The M203 would ultimately replace the M79, but the M79 has remained in service in many units worldwide in niche roles.

 The M79 grenade launcher was a result of Project Niblick, an attempt to increase firepower for the infantryman by having an explosive projectile more accurate with further range than rifle grenades, but more portable than a mortar. Project Niblick created the 40 x 46 mm grenade, but was unable to create a satisfactory launcher for it that could fire more than a single shot. One of the launchers at Springfield Armory was the single-shot break-open, shoulder-fired S-3. It was refined into the S-5. Unable to develop a suitable multi-shot launcher, the Army adopted the S-5 as the XM79. With a new sight, the XM79 was officially adopted as the M79 on December 15, 1960.

 In 1961, the first M79 grenade launchers were delivered to the US Army. Short in length and relatively light in weight, the M79 became popular among American soldiers in Vietnam. A grenadier using a M79 could consistently drop grenades into a garbage can 150 yards away. However, its single-shot nature was a strong drawback.

 The M79 grenade launcher is simple in design, having only five parts: a receiver group, a fore-end assembly, a barrel group, a sight assembly, and a stock. The fore-end assembly beds the barrel to the receiver. The stock is made out of wood or fiberglass. A rubber pad affixed to the shoulder stock to absorbs some recoil. The front sight is a fixed blade. The rear sight on the M79 is a folding ladder-style leaf-type sight. When folded, the leaf sight acts as a fixed sight for close range. A grenadier may simply point and shoot with high accuracy. When unfolded, the leaf-type sight could be adjusted for ranges from 75-meters to 375-meters, in 25-meters increments.

 The M79 grenade launcher is easy to operate. To load, the grenadier pushes the barrel locking latch on the receiver group to the right. Gravity will pull down the barrel, breaking it open, and exposing the breech. The hammer is cocked when the breech is opened. A round then may be loaded. The break action must then be closed manually. Closing the breech will cause the barrel locking latch to return to center. To fire, the grenadier pushes the safety forward, revealing the symbol 'F', and pulls the trigger. To unload, the grenadier pushes the barrel locking latch to the right and opens the breech. The extractor will push the case out, allowing the grenadier to grasp it and remove it.

 Many different ammunition types were produced for the M79 and subsequently for the M203 grenade launchers, outside of the smoke and illumination rounds three main types emerge: Explosive, Close-range, and Non Lethal Crowd Control. The break-open action of the M79 allows it to use longer rounds that the standard M203 cannot use.

 The M406 40 mm HE (high explosive) grenades fired from the M79 travel at a muzzle velocity of 75 meters per second. The M406 contained enough explosive to produce over 300 fragments that travel at 1,524 meters per second within a lethal radius of 5 meters. This round incorporated a spin-activation safety feature which prevents the grenade from arming while still within range of the shooter; it armed itself after traveling a distance of about 30 meters.

 For close range fighting two styles of M79 grenade launcher rounds were developed. The first was a flechette or Bee Hive round which fired 45 10-grain steel flechettes. Flechettes proved to be ineffective because they would often not hit point-first and penetrate. About 1966, this was replaced by the M576 buckshot round. Containing twenty (M576E1) or twenty-seven #4 buckshot (M576E2), this round could be devastating at close ranges. However, as range increased, the shot spreads out so rapidly as to be ineffective.

 The M79 grenade launcher has been used extensively also for crowd control purposes where it is desirable to have a weapon dedicated solely to less-lethal force. The three common less-lethal rounds are the M651 CS gas, the M1029 sponge grenade, and the M1029 Crowd Dispersal rounds.

 The M79 has seen notable limited use during Operation Iraqi Freedom, such as for clearing IEDs.

 M203 refers to the United States Army designation for a single shot 40 mm grenade launcher that attaches to the M16 assault rifle or the M4 Carbine.

 The M203 grenade launcher attaches under the barrel and forward of the magazine, the trigger being just forward of the rifle magazine. The rifle magazine functions as a hand grip when firing the M203. A separate sighting system is added to rifles fitted with the M203, as the rifle's standard sights are not matched to the launcher. The M203 can fire high-explosive, smoke, illuminating, buckshot direct fire, CS gas, and training grenades.

 The M203 grenade launcher was designed as a rifle attachment in order to increase the efficiency at which a soldier could alternate between bullet fire and High Explosive grenade fire.

 The M203 Grenade launcher system comes with a variety of components, usually including the launcher, adaptors for attachment to assault rifles, and leaf sights (which can be used with the rifle's front sight post). M203s can also come with quadrant sights, mounting to a MIL-STD 1913 Rail, or to the carrying handle of an M16 rifle.

 There are numerous variants of the M203 manufactured in the U.S., and throughout the world, for various applications. These vary chiefly in the length of the barrel, attachment type, and quick detach (QD) capability.

 The standard M203 grenade launcher is intended for permanent (armorer level) attachment to the M16A1, M16A2 and M16A3 rifles, and utilizes a 12" rifled barrel. These can also be attached to M4 and M4A1 carbines, using a different front attachment point forward of the front sight block, but the SOPMOD kit uses M203A1 grenade launchers.

 The American M203A1 grenade launcher is intended for use with the M4 and M4A1 Carbine. The barrel is shortened to 9", and principally the M203A1 QD is able to quickly detach from the rifle, and be replaced by a Knight's Armament Company M4 RAS lower handguard. An advantage of using a 40 mm grenade launcher on an assault rifle equipped with MIL-STD 1913 Rails is the attachment of various range-finding optics.

 The M203A2 grenade launcher is intended for use with the M16A4 MWS (Modular weapon system). Using standard 12" barrels, the grenade launcher is intended for use in concert with the Knight's Armament Company M5 RAS. Again, an advantage of this system is the attachment of range-finding optics makes precision targeting easier.

 The M203 grenade launcher has proved vastly popular worldwide and inevitably has been fitted to a number of weapon systems other than the M16 rifle/M4 carbine for which it was designed.
  These include:
Steyr AUG- In Australian and New Zealand service.
SG 550 and Galil SAR- In Chilean service and Special Forces.
Steyr Aug- in Irish service.
AK-47/AKM- In Israeli service.
Galil SAR- In Israeli service.
Tavor TAR-21- In Israeli service.
Bernardelli VB/VB-SR - In Italian service.
STK SAR-21- In Singaporean service.
Ak 5- In Swedish service.

 In the United States, M203 grenade launchers are classified as "Destructive Devices" under the National Firearms Act subject to the NFA process. M203s are not that common in the civilian NFA market because each explosive 40 mm grenade is also subject to the NFA process and its subsequent $200 tax.

 A new grenade launcher in development, the XM320, will likely replace the 203 in United States service eventually. The XM320 weighs more than the M203, but has some added benefits.