M class or M-class may refer to:

Military

M-class cruiser, a planned German light cruiser class
M-class destroyer, several classes of destroyer
- Admiralty M-class destroyer, a class of British destroyers built 1913–1916 and served in World War I
- M-class, British destroyers starting with the letter M of the L and M-class destroyer, launched 1939–1942 and served in World War II
- Marcílio Dias-class destroyer, Brazilian destroyers built during World War II
Karel Doorman-class frigate, of the Royal Netherlands Navy
M-class minesweeper, several classes of minesweeper
- M-class minesweeper (Germany), a class of minesweepers of the World War II German Kriegsmarine
- M-class minesweeper (Netherlands), a class of minesweepers of the Royal Netherlands Navy built after World War I
Abercrombie-class monitor, a British WWI class of monitor gunships
M-class submarine, several classes of submarine
- British M-class submarine
- United States M-class submarine

Transportation

Mercedes-Benz M-Class, an automobile
M-segment, a European vehicle size class
NZR M class locomotives
Pennsylvania Railroad class M1, locomotives
Victorian Railways M class, steam locomotives
Victorian Railways M class (diesel-hydraulic), shunting locomotives
OOCL M-class container ship, a class of large container ships operated by Orient Overseas Container Line
Maersk M-class container ship, a class of large container ships operated by Maersk Line