The COP .357 is a 4-shot Derringer-type pistol chambered for .357 Magnum. The double-action weapon is about twice as wide, and substantially heavier than the typical .25 automatic pistol, though its relatively compact size and powerful cartridge made it an option for a defensive weapon or a police backup gun. It was designed by Robert Hillberg, based on his earlier work on the Hillberg Insurgency Weapon. It was manufactured by the now defunct COP Inc. of California, US (COP stood for Compact Off-Duty Police). In 1990 it was manufactured by American Derringer for a short time.

The COP .357 is quite robust in design and construction. It is made of solid stainless steel components. Cartridges are loaded into the four separate chambers by sliding a latch that "pops-up" the barrel for loading purposes, similar to top-break shotguns.

A smaller caliber version the "MINI COP" was also manufactured in .22 Magnum.