MJ may refer to:
Mjolnir ( MOHL-n(ee)r) is a fictional weapon appearing in American comic books published by Marvel Comics.
mjunction services limited is a 50:50 joint venture of two Indian steel conglomerate – the Steel Authority of India Ltd (SAIL) and Tata Steel.
Mjøsa is Norway's largest lake, as well as one of the deepest lakes in Norway and in Europe. It is the fourth-deepest lake in Norway.
MJP Architects is an employee-owned British architectural practice established in 1972 by Sir Richard MacCormac, and based in Spitalfields, London.
MJM Music PL, is a Polish independent record label founded in 1990 in Warsaw by Polskie Radio journalist Andrzej Wojciechowski.
Mjällby Allmänna Idrottsförening, also known simply as Mjällby AIF, Mjällby or (especially locally) MAIF, is a Swedish professional football club based in Hällevik.