Mark IV or Mark 4 often refers to the fourth version of a product, frequently military hardware. "Mark", meaning "model" or "variant", can be abbreviated "Mk."

Mark IV or Mark 4 may refer to:

Computers

• MARK IV (software), a 1960s-era 4th-generation programming language from Informatics
• Harvard Mark IV (1952), an all-electronic stored-program computer
• Emergency Medical Hologram Mark IV, in Star Trek: Voyager, an artificially intelligent medical program

Music

• The Mark IV, American vocal group, 1950s
• The Mark Four (1966–1968), an English band
• MARK IV (Barbershop), a barbershop quartet that won the 1969 SPEBSQSA competition
• Mesa Boogie Mark IV (1993–2008), an electric guitar amplifier
• Disklavier § Mark IV, a reproducing piano sold by Yamaha Corporation

Religion

• Mark 4 or Mark IV, the fourth chapter of the Gospel of Mark in the New Testament of the Bible
• Patriarch Mark IV of Alexandria, Greek patriarch of Alexandria in 1385–1389
• Pope Mark IV of Alexandria (died 1363), Coptic Pope in 1348–1363

Vehicles

• Mark 4 (Iarnród Éireann), Irish Rail InterCity train
• Mark IV monorail, train used at Walt Disney World, 1971–1989
• Mark IV tank, an up-armoured variant of the British Mark I tank, 1917
• Bristol Blenheim Mk.IV, light bomber in Royal Air Force service before and during World War II
• British Rail Mark 4, passenger train
• Chandelle Mk IV, ultralight aircraft
• Cozy MK IV, an experimental 4 place canard aircraft derived by Nat Puffer from the Burt Rutan Long-EZ
• Jaguar Mark IV (1945–1949), British car
• Continental Mark IV (1959, 1972–1976), American luxury car
• Merkava Mark IV (1999), main battle tank of Israel Defense Forces
• Triumph Spitfire, MKIV (1970–1974), a British sports car

Weapons

• Webley Mk IV, a.k.a. "Boer War Model"; .455 caliber British revolver from 1899
• MK IV Series 80 M1911 pistol, semi-automatic pistol
• Mark 4 nuclear bomb (1949–1953), an American nuclear bomb

Other

• Canon EOS-1D Mark IV, a digital SLR
• Navy Mark IV (late 1950s–early 1960s), a full pressure suit designed for unpressurized military jets
• Vickers Tank Periscope MK.IV (1936), designed in Poland
• Mk IV Turtle helmet (1950s–1980s), British Army helmet, a slight design change from the Mk III Turtle helmet