IJ may refer to:
- IJ (digraph), the ligature of the letters I and J
- IJ (Amsterdam), a body of water near Amsterdam, Netherlands
- Ij, Iran, a city in Fars Province, Iran
- Ij, Semnan, a village in Semnan Province, Iran
- IJmeer, a lake in the Netherlands
- immigration judge
- in genetics, the Y-DNA Haplogroup IJ
- Ike Jarlego, Filipino film editor and director
- Indiana Jones
- Infinite Jest
- Institute for Justice, a United States non-profit libertarian public interest law firm, specializing in pro bono support of individuals to engage in free enterprise without obtaining what it considers "unnecessary" licensing or regulatory compliance
- Internal jugular vein
- short form for Convent of the Holy Infant Jesus (CHIJ)
- iJustine
- IJ (motorcycle), popular motorcycle in Russia
- Great Wall Airlines IATA code
- İj River, a Tatar spelling for the Izh River