M21

M21 or M-21 may refer to:

Transportation

 * M21 (New York City bus), a New York City Bus route in Manhattan
 * M-21 highway (Michigan), a road connecting Flint and Grand Rapids
 * M21 (East London), a Metropolitan Route in East London, South Africa
 * M21 (Pretoria), a Metropolitan Route in Pretoria, South Africa
 * M21 (Durban), a Metropolitan Route in Durban, South Africa
 * Highway M21 (Ukraine)

Military

 * HMS M21, Royal Navy M15 class monitor; sunk in 1918
 * M21 mine, an American circular anti-tank landmine
 * M21 Sniper Weapon System, a sniper rifle based on the M14 rifle
 * Zastava M21, a Serbian assault rifle
 * the carrier aircraft for the Lockheed D-21
 * M21 Mortar Motor Carriage, a Half-Track carrying an 81mm Mortar

Other

 * BMW M21, a 1983 2.4 L diesel straight-6 engine
 * MSrE M-21, Hungarian aerobatics aircraft
 * Lockheed M-21, an American reconnaissance drone carrier aircraft
 * MacGregor 21, an American sailboat design
 * Messier 21, an open star cluster in the constellation Sagittarius
 * Proton Putra, car model sold in Australia as Proton M21
 * M postcode area, M21 Chorlton-cum-Hardy, Firswood area of Manchester