M51

M51 or M-51 may refer to:


 * M-51 (Michigan highway), a state highway in Michigan
 * M51 highway (Russia)
 * M51 (Cape Town), a Metropolitan Route in Cape Town, South Africa
 * M51 Skysweeper, an anti-aircraft gun
 * M51 MACI mine
 * M51 SLBM, a French nuclear ballistic missile
 * BMW M51, a 1991 straight-6 Diesel engine
 * Sherman M-51, an Israeli modification of American M4 Sherman tank
 * Eidgenössischer Stutzer 1851, a historical service rifle of the Swiss Army
 * Messier 51, a spiral galaxy also known as the Whirlpool Galaxy
 * Samsung Galaxy M51, a smartphone released in 2020