Break action is a type of firearm action in which the barrel(s) are hinged much like a door and rotate perpendicularly to the bore axis to expose the breech and allow loading and unloading of cartridges. A separate operation may be required for the cocking of a hammer to fire the new round. There are many types of break-action firearms; break actions are universal in double-barreled shotguns, double-barreled rifles, combination guns, and are commonly found in single shot pistols (especially derringers), rifles, shotguns, including flare guns, grenade launchers, air guns, and some older revolver designs. They are also known as hinge-action, break-open, break-barrel, break-top, or, on old revolvers, top-break actions.

The first break-action revolver was patented in France and Britain at the end of December in 1858 by Devisme. A substantial hinge pin joins the two parts of the rifle or shotgun; the stock with its firing mechanism and the fore-piece and barrel, which hold the round to be fired. In some cases the hinging pin may be easily removable, allowing the two portions of the weapon to be compactly and safely stored. In other cases the hinge will consist of a hook over a pin; releasing an auxiliary latch will allow sufficient travel to allow the hinge to be unhooked.

A latch is operated to release the two parts of the weapon, allowing the breech to be exposed. Rounds are inserted into the breech, loading as many barrels (pistol, rifle, or shotgun) or chambers (revolver) as desired, and the mechanism is closed and latched. The hammer is then pulled back and latched. The weapon can now be fired by squeezing the trigger.

After firing the rounds, the break action is unlatched and the barrel and forearm are allowed to fall forward. This causes an extractor catch to remove the spent shells so that they fall to the ground, leaving the weapon ready for reloading.

The tip-up was the first revolver designed for use with metallic cartridges in the Smith & Wesson Model 1, on which the barrel pivoted upwards, hinged on the forward end of the top strap. On S&W tip-up revolvers, the barrel release catch is located on both sides of the frame in front of the trigger.

A break action is one of the most compact firearm actions. Since there are no parts to reciprocate, it is shorter than repeating designs, and generally more compact than other non-repeating firearms such as falling block and rolling block actions. This compactness results in reductions in weight and size compared to larger actions; this can also allow a longer barrel in a firearm of similar size.

Since the cartridge extractor or ejector is built into the barrel assembly in break action weapons, the breech face is simply a flat plate with a hole for the firing pin to protrude through. This makes break actions ideal for interchangeable barrel firearms, such as the popular Thompson/Center Arms Contender and Encore pistols. The simplicity of the break-open design, especially with an external hammer, also reduces the cost of manufacture. There were a number of companies, such as H&R Firearms, that produced break-action rifles at lower costs than comparable bolt-action rifles.

While most firearms are designed for right-handed shooters, break-action guns operate identically when fired from either shoulder.