M40 or M-40 may refer to:

Transportation M40 motorway, a motorway in England M-40 (Michigan highway), a state highway in Michigan, US M40 (Cape Town), a Metropolitan Route in Cape Town, South Africa M40 (Johannesburg), a Metropolitan Route in Johannesburg, South Africa M40 (Pietermaritzburg), a Metropolitan Route in Pietermaritzburg, South Africa Autopista de Circunvalación M-40, a motorway in Madrid, Spain BMW M40, a 1987 automobile piston engine Charomskiy M-40, an aircraft engine Volvo M40 transmission, an automobile transmission Chiltern Railways, previously known as M40 Railways

Science Messier 40 (M40), a double star in the constellation Ursa Major the 40th Mersenne prime

Firearms and military equipment M40 field protective mask, a United States military gas mask M40 rifle, a sniper rifle M40 gun motor carriage, a United States self-propelled artillery vehicle M40 recoilless rifle, an anti-tank gun M/40 automatic cannon, a Swedish heavy machine gun Macchi M.40, a prototype 1920s Italian catapult-launched reconnaissance seaplane The incorrect designation for the SSh-40, a Russian infantry helmet A collector's term for later versions of the M1935 Stahlhelm

Athletics M 40, an age group for Masters athletics (athletes aged 35+)

Technology

Samsung Galaxy M40, a smartphone

Arts and entertainment M40, a song by Aitch from the album 4

See also 40M (disambiguation)