The Mk 23 is a modern large caliber pistol of German origin. It was developed in the early 1990's by Heckler & Koch as a contender for the Offensive Handgun Weapon System program. This program was to supply US special forces with a pistol powerful and accurate enough to be used as both an offensive and backup weapon. Despite its qualities the size and weight meant that other types of pistols remained in US special forces service alongside the Mk 23. The Mk 23 forms the basis for the highly succesful USP pistol, introduced 2 years later.

The Mk 23 is a large high quality short recoil double action pistol. It has a long barrel with polygonal rifling and muzzle threaded to accept a suppressor. The Mk 23 pioneered the use of a polymer frame, which houses a double stack magazine and accessory rails. The suppressor and laser aiming module were developed specifically for the Mk 23.

The Mk 23 fires the powerful .45 ACP round from 12 round magazines. When introduced this was considered a high capacity magazine in this caliber. The subsonic nature of the .45 ACP makes it ideal for use with a suppressor. Accuracy of the Mk 23 is reported to be very good. Around 4 MOA can be expected at 50 meters, making the Mk 23 more practical for use beyond 25 meters than most other combat pistols.

The Mk 23 was adopted by US SOCOM and was issued to various US special forces units. Various special forces units around the world adopted the Mk 23 in small numbers. Nowadays the Mk 23 remains available, but more practical alternatives are favored. These include newer Heckler & Koch products such as the USP Tactical and HK 45.