Mess dress uniform is the most formal (or semi-formal, depending on the country) type of uniforms used by military personnel, police personnel, and other uniformed services members. It frequently consists of a mess jacket, trousers, white dress shirt and a black bow tie, along with orders and medals insignia. Design may depend on regiment or service branch, e.g. army, navy, air force, marines, etc. In Western dress codes, mess dress uniform is the supplementary alternative equivalent to the civilian black tie for evening wear or black lounge suit for day wear although military uniforms are the same for day and evening wear. Mess dress uniforms are typically less formal than full dress uniform, but more formal than service dress uniform.

Prior to World War II, this style of military uniform was largely restricted to the British and United States Armed Forces, although the French, German, Swedish and other navies had adopted their own versions of mess dress during the late 19th century, influenced by the British Royal Navy.

While mess dress uniform is predominantly worn at occasions by commissioned officers and non-commissioned officers, it may also be worn as an optional uniform by some senior enlisted personnel. It is also sometimes worn by members of royal courts or certain civilian uniformed services.