JJ or jj may refer to:

• J. J. Evans, a character in the 1970s sitcom Good Times
• Jennifer Jareau or JJ, a character on Criminal Minds
• "JJ", an episode of Skins series 4
• JJ DiMeo, a character on Speechless
• John Diggle Jr., a character from the TV series Arrow nicknamed "J.J."
• "JJ" (Skins series 3), a 2009 episode of Skins series 3
• JJ, the production code for the 1967 Doctor Who serial The Macra Terror
• Jean-Jacques Leroy, a character in the 2016 anime Yuri on Ice

• "J.J.", a song on the soundtrack of the video game L.A. Noire
• JJ (Swedish band)
• JJ, a band featuring English singer Jan Johnston
• J.J.!, an album by J. J. Johnson
• Abbreviation for Latin Jesu Juva, used by Johann Sebastian Bach at the beginning of his compositions
• JJ (singer), the stage name of Austrian-Filipino singer-songwriter Johannes Pietsch

• JJ (magazine), a fashion magazine
• JJ (video game), a video game developed and published by Square Co., Ltd.

• JJ Lin (born 1981), Singaporean artist
• Jermaine Jenas (born 1983), English footballer
• John Jay (1756–1829), American diplomat and judge
• Junaid Jamshed or JJ (1964–2016), Pakistani religious figure
• Justo Justo or JJ (1941–2012), Filipino columnist and news presenter
• J. J. Eubanks (born 1968), American basketball player
• JJ Kaplan (born 1997), American-Israeli basketball player
• JJ Lehto (born Jyrki Juhani Järvilehto, 1966), Finnish motor racing driver
• J. J. McCarthy (born 2003), American football player
• JJ Pegues (born 2001), American football player
• J. J. Valberg (born 1936), British-American philosopher
• J. J. Webster (1898–1965), American politician
• Joanna Jędrzejczyk or JJ (born 1987), Polish MMA fighter

• Jj coupling, a form of angular momentum coupling
• JJ, a brassiere measurement in the UK
• LATAM Brasil, formerly TAM Airlines (IATA code JJ)
• J/Z (New York City Subway service), formerly JJ
• JJ, abbreviation for plural judges, justices
• JJ, rapid trains on the Jōban Line in Japan
• Jilly Juice, a fermented drink and a form of alternative medicine
• John Jay Hall, a dormitory at Columbia University

• Jay Jay the Jet Plane, a children's television cartoon series
• Jay Jay, a 2003 Tamil film
• Jay-J (born 1969), American house music disc jockey
• Double J (disambiguation)
• J & J (disambiguation)
• JJS (disambiguation)
• GG (disambiguation)
• JJJ (disambiguation)