The letter combination IJ is:
* the ligature of the letters "I" and "J". In Dutch it usually represents the diphthong IPA| [eɪ] or IPA| [ɛɪ] , and is sometimes considered be to be a single letter: see IJ (digraph).When used to represent this digraph, IJ can stand for:
* IJ (bay), a body of water near Amsterdam, Netherlands

As an abbreviation, IJ can stand for:
* in genetics, the Y-DNA Haplogroup IJ
* Indiana Jones
* Institute for Justice
* Internal jugular vein

As a code, IJ can be:
* Great Wall Airlines IATA code

*İj River, a Tatar spelling for the Izh River

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