IFF, Iff or iff may refer to:
Arts and entertainment
- Simon Iff, a fictional character by Aleister Crowley
- Iff of the Unpronounceable Name, a fictional character in the Riddle-Master trilogy by Patricia A. McKillip
- "IFF", an episode of The Expanse
Mathematics, science, and technology
- Identification friend or foe, an electronic radio-based identification system
- If and only if, a biconditional logical connective between statements, where either both statements are true or both are false
- IFF (software), a series of compositing and visual effects applications (Inferno, Flame and Flint) made by Autodesk Media and Entertainment
- Iff card, a smart card used on bus services in Cardiff, Wales, United Kingdom
- Interchange File Format, a computer file format
Organizations
- Institute For Figuring, an organization that promotes the public understanding of the poetic and aesthetic dimensions of science, mathematics and the technical arts
- International Federation of Factory Workers, former trade union international
- International Flavors & Fragrances, an American corporation which produces flavors and fragrances
- International Freedom Foundation, a self-described anti-communist group established in Washington, D.C.
- Iff Books, an imprint of John Hunt Publishing
Sports organizations
- International Fencing Federation (Fédération Internationale d'Escrime or FIE), the international governing body for fencing
- International Floorball Federation, the global governing body for the sport of floorball
- Irish Fencing Federation, the governing body for fencing in Ireland
Other uses
- Fakultät für Interdisziplinäre Forschung und Fortbildung (Faculty for Interdisciplinary Research and Continuing Education), a faculty of the Austrian University of Klagenfurt
- Indonesian Film Festival, an annual awards ceremony organised by the Indonesian Film Board to celebrate cinematic achievements in the Indonesian film industry
- International Finance Facility, proposed by HM Treasury in conjunction with the Department for International Development of the United Kingdom
- International freight forwarder, an individual or company that books or otherwise arranges space for shipments between countries via common carriers