MJ

MJ may refer to:

• Manufacturers' Junction Railway's reporting mark
• Líneas Aéreas Privadas Argentinas' IATA code
• Jeep Comanche or MJ, a pickup truck
• Millijoule (mJ) or megajoule (MJ), units of energy
• MJ, a defunct New York City subway service
• M_J, Jupiter mass, a unit of mass
• Master of Jurisprudence, a graduate law degree
• MJ, citation abbreviation for West's Military Justice Reporter
• Marijuana