AJ, or variants, may refer to:
Arts, entertainment and media
Fictional characters
Applejack (My Little Pony: Friendship Is Magic), a character from the fourth incarnation of My Little Pony
A. J. (The Fairly OddParents), a fictional character
A.J. Simon, a character in the American crime drama television series Simon & Simon
A.J. Soprano, a fictional character in The Sopranos
Superspinner AJ, a fictional character in the Starflyers series of computer games
AJ, in AJ and the Queen, an American comedy-drama TV series
Apollo Justice, a fictional character from Apollo Justice: Ace Attorney
AJ, a character from Blaze and the Monster Machines
Literature
Architects' Journal, an architectural magazine
The Astronomical Journal, a peer-reviewed monthly scientific journal
Media
Aj (newspaper), a Hindi-language daily broadsheet newspaper in India
Businesses and organisations
Al Jazeera Arabic, a Qatar-based international Arabic news channel
AJ+, an online news and current events channel
AJ Capital Partners, an American private real estate company
AJ's Fine Foods, an American supermarket chain
AJ Institute of Engineering and Technology, in Mangalore, India
Technology
Jaguar AJ-V8, a line of V8 engines manufactured by Jaguar
Other uses
Adherens junction, a protein complex
AJ (given name), including a list of people with the name or nickname
aJ, attojoule, a unit of energy equal to 10−18 joules
Australian Scout Jamboree, a triennial festival
North American AJ Savage, an aircraft
Azerbaijan, WMO, FIPS, LOC MARC and obsolete NATO country code
Animal Jam Classic, an online game formerly known as Animal Jam
Animal Jam, an online mobile game formerly known as Animal Jam - Play Wild!