The Suomi KP/-31 (Suomi-konepistooli or 'Submachine-gun Finland') was a submachine gun (SMG) of Finnish design that was in service during World War II. It was a descendant of the M-22 prototype and the KP/-26 production model, which was revealed to the public in 1925. The Suomi-konepistooli KP/-31 is often abbreviated to Suomi KP.
The Suomi KP was also manufactured under licence in Sweden, Denmark, and Switzerland, where it was known as the Hispano-Suiza MP43/44.
In 2009, a semi-automatic version of the Suomi KP was produced for civilian sale in the United States, replacing the receiver and lengthening barrel to meet the standards of the National Firearms Act.
A Suomi submachine gun is the weapon used by a mass murderer in the Sjowall/Wahloo Swedish mystery novel The Laughing Policeman. In the novel, a character asks if the weapon is the Finnish version or the Swedish-licensed version. A detective says a Finnish-made version, though he uses the Swedish model number (m/37) in mentioning it.