Military rank is a system of hierarchical relationships in armed forces or civil institutions organized along military lines. Usually, uniforms denote the bearer's rank by particular insignia affixed to the uniforms. Ranking systems have been known for most of military history to be advantageous for military operations, in particular with regards to logistics, command, and coordination; as time continued and military operations became larger and more complex, military ranks increased and ranking systems themselves became more complex.

Within modern armed forces, the use of ranks is almost universal. Communist states have sometimes abolished rank (e.g., the Soviet Russian Red Army 1918–1935, the Chinese People's Liberation Army 1965–1988, and the Albanian Army 1966–1991), only to re-establish them after encountering operational difficulties of command and control.

Ancient and medieval ranks