A choke is a tapered constriction of a firearm barrel at its muzzle end. Chokes are most commonly seen on shotguns, but are also used on some rifles, pistols, or even airguns.

Chokes are almost always used with modern hunting and target shotguns to improve performance. Their purpose is to shape the spread of the shot "cloud" or "string" to gain better range and accuracy, and to deliver the optimum pattern of pellet density, for the particular target, depending on its size, range, aspect and whether it is traveling towards, across or away from the shooter. Chokes are implemented as either screw-in chokes, selected for particular applications, or as fixed, permanent chokes, integral to the shotgun barrel.

Chokes may be formed at the time of manufacture either as part of the barrel, by squeezing the end of the bore down over a mandrel, or by threading the barrel and screwing in an interchangeable choke tube. Chokes may also be formed even after a barrel is manufactured by increasing the diameter of the bore inside a barrel, creating what is called a "jug choke", or by installing screw-in chokes within a barrel. However implemented, a choke typically consists of a conical section that smoothly tapers from the bore diameter down to the choke diameter, followed by a cylindrical section of the choke diameter. Briley Manufacturing, one maker of interchangeable shotgun chokes, uses a conical portion about 3 times the bore diameter in length, so that the shot is gradually squeezed down with minimal deformation. The cylindrical section is shorter and usually between 15 and 19 mm (0.6 to 0.75 inches) in diameter.

A choke is designed to alter or shape the distribution of the shot as it leaves the firearm. For shooting most game birds and clay pigeons, a desirable pattern is one that is as large as possible while being dense enough to ensure multiple hits on the target, at a particular range. The choke should be tailored to the range and size of the targets. Shotguns intended for defensive use often have cylinder or improved cylinder chokes for the widest shot pattern at typically short defensive ranges; "cylinder barrels" have no constriction.

A skeet shooter shooting at close crossing targets might use 0.13 mm (0.005 in) of constriction to produce a 75 cm (30 in) diameter pattern at a distance of 20 m (22 yd). A trap shooter shooting at distant targets traveling away from the gun might use 0.75 mm (0.030 in) of constriction to produce a 75 cm (30 in) diameter pattern at 35 m (38 yd). Special chokes for turkey hunting, which requires long range shots at the small head and neck of the bird, can go as high as 1.5 mm (0.059 in).

The use of too much choke and a small pattern increases the difficulty of hitting the target; the use of too little choke produces large patterns with insufficient pellet density to reliably break targets or kill game.

As far back as 1787 a Frenchman by the name of M. Magne de Marolles gave an account of choke-boring, though he argued against it.

Some sources state that the first pioneer was a Czech named Dominik Brandejs, who made shotguns with a choke in order to reduce the dispersion of shots, but his design was not popular in the 1820s.