Type: Semi-automatic handgun
Origin: Germany
Year: ~1996
Length: 245.11 mm (9.65 in)
Barrel length: 149.10 mm (5.87 in)
Weight: 1.2 kg (2.43 lb), empty
Caliber: .45 ACP
Capacity: 12 rds

The HK MK 23, marketed as the Mark 23 on the civilian market, is a semi-automatic pistol developed by German firearms manufacture Heckler & Koch. The pistol was designed to meet specifications for a new, larger caliber handgun set by US Special Operations Command (USSOCOM) in the early 1990s. After successfully defeating competing designs, the MK 23 was adopted by the USSOCOM with the first deliveries reaching units in 1996. In military service, the new pistol was part of a complete system including a hard case, a suppressor, and a laser aiming module. The civilian version, however, was offered as just the pistol. Civilian models were also initially offered with a 10 round magazine in order to comply with the 1994 Assault Weapons Ban in the United States; however, 12 round magazines are now sold for/with the pistol except in states which continue to impose magazine capacity restrictions. While an excellent weapon, the MK 23/Mark 23 drew criticism due to large size and weight with newer pistol designs, including HK's own USP Tactical, offering the same level of performance in a smaller and lighter package.