The term derringer is a genericized misspelling of the last name of Henry Deringer, a famous maker of small pocket pistols in the 1800s. Many copies of the original Philadelphia Deringer pistol were made by other gun makers worldwide, and the name was often misspelled; this misspelling soon became a generic term for any pocket pistol. The original Deringer pistol was a single shot muzzleloading pistol; with the advent of cartridge firearms, pistols began to be produced in the modern form still known as a "derringer".

A derringer is generally the smallest usable handgun of a given caliber. They were frequently used by women because they are easily concealable in a purse, or as a stocking gun. Derringers are not repeating firearms—repeating mechanism such as used on semiautomatic handguns or revolvers would add significant bulk to the gun, defeating the purpose. The original cartridge derringers held only a single round, usually a pinfire or rimfire cartridge, usually around a .40 caliber, and the barrel pivoted sidways on the frame to allow access to the breech for reloading. The famous Remington derringer design doubled the capacity, while maintaining the compact size, by adding a second barrel on top of the first, and pivoting the barrels upwards to reload. Each barrel then held one round, and a cam on the hammer alternated between top and bottom barrels. The Remington derringer was in .41 Rimfire short caliber, and achieved wide popularity. The .41 Rimfire bullet moved very slowly at about 425 feet per second (130 m/s or about 290 mph or 470 km/h). It could be seen in flight but at very close range (such as at a casino or saloon card table) it could easily kill. It was sold from 1866 to 1935.

Even with the advent of smaller, higher powered cartridges made possible by the use of smokeless powder rather than the black powder used in the 1800s and before, the classic Remington design is still popular; a Remington pattern derringer in .38 Special is still smaller than the most compact .25 ACP semiautomatic, and provides far superior terminal ballistic performance in its 2 shots than the .25 ACP does with 6 or 7. While the classic Remington design is a single action, manufacturers have also made double action derringers, including some 4 shot models, with the barrels stacked in a 2 x 2 block. The "COP" derringer, made in Torrance, CA, provided 4 shots of .357 Magnum, still in a package not much larger than a .25 ACP automatic, and significantly more compact than a similar revolver. The COP derringer was invented by Robert Hillberg and closely resembled his earlier work on insurgency weapons.

Despite their stopping power advantage over most "pocket guns," modern derringers rarely are seen for sale in gun shops. Instead, a whole variety of similarly-sized .32 ACP and .380 ACP semiautos, notably the Kel-Tec P-32, selling to that market are what gun stores mainly have in their display counters for customers wanting truly tiny handguns now, as they carry up to 8 rounds instead of a derringer's 2 while being far faster to reload and shooting similar-power ammo.

A related design, often grouped with derringers since it fits no other standard classification, is the Semmerling pistol. It is a 5 shot, .45 ACP pistol and a manual repeater; the barrel mechanism is manually pulled forward to eject the fired round, then pushed back to chamber the next round. These pistols were originally built for the U. S. Army, and the few available on the civilian market are highly sought after due to their unique combination of high power, large capacity, and tiny size. Another military pistol that is truly a derringer design is the Liberator Pistol, a .45 ACP insurgency weapon dropped behind Axis lines in WWII.

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