The Heckler and Koch submachine gun, MP5, is one of the most famous and wide-spread firearms of its class, developed since the Second World War. Its development began circa 1964 under the company designation HK MP-54, or simply HK 54. In 1966, the German police and the Border Guard adopted the HK 54 as the MP5. Over the years, the MP5 was adopted by a huge number of police, security, and military forces around the world, including the German police and border guard, the British police and the elite army SAS units, the American police, the FBI, the Navy and the Marine Corps
There are many variations on the German MP5, including the MP5k (Kurz - the German word meaning short) that was designed for CQB, the MP5-PDW, a modification on the MP5 designed for personal defence, and the SP89, designed for civilian use, it is semi-automatic, and has a different grip. For a complete list see here.