In order to fire a handgun, two specific actions must take place. Step 1: The mainspring must be compressed to generate potential energy. This is often done by cocking the hammer. Some handguns, however, do not have hammers, and the mainspring is directly connected to a spring-loaded striker (the firing pin). Step 2: The mainspring must be released, converting the stored potential energy to mechanical energy. All handguns (revolvers, semi-automatic pistols, and Derringers) must perform these two steps in order to discharge the cartridge. The action of a handgun refers to the mechanism used to perform these steps.

There are three general types of actions commonly used on handguns, each performing the two basic steps slightly differently.

When the trigger is pulled on a single action handgun, it performs only Step 2 —release of the hammer from its cocked position. In single action handguns, the hammer must be cocked manually (Step 1).

When the trigger is pulled on a double action handgun, both Steps 1 and 2 are performed. The hammer is cocked and then released by pulling the trigger. Since the process of cocking the hammer compresses the mainspring, the force that must be applied to the trigger of a double action handgun is greater than that of a single action gun. The hammer of a double action handgun, however, can be manually cocked.

Double action-only handguns function essentially the same way as double action handguns, except it is not possible to manually cock the hammer.