IFF, Iff or iff may refer to:
Technology/Science:
- Identification friend or foe, an electronic radio-based identification system using transponders
- Interchange File Format, a computer file format introduced in 1985 and later extended into many others
- IFF (software), a series of compositing and visual effects applications (Inferno, Flame and Flint) made by Autodesk Media and Entertainment
- if and only if, a mathematical and logical connector indicating that either both statements are true or both are false
Transport:
- Iff card, a smart card used on bus services in Cardiff, Wales
Other:
- Institute For Figuring, an organization that promotes the public understanding of the poetic and aesthetic dimensions of science, mathematics and the technical arts
- International Fencing Federation, the English name of the international governing body for fencing, the Fédération Internationale d'Escrime
- International Floorball Federation, the global governing body for the sport of floorball
- International Flavors and Fragrances, a company producing flavors and fragrances
- International Freedom Foundation
- International Film Festival
- International Finance Facility
- International Freight Forwarder, an individual or company that books or otherwise arranges space for shipments between countries via common carriers
- Irish Fencing Federation, the governing body for fencing in Ireland
- Fakultät für Interdisziplinäre Forschung und Fortbildung (IFF), Interdisciplinary Faculty of the Austrian University of Klagenfurt
Military
- Identification Friendly Forces, a patch worn by soldiers, sometimes shown/not shown to I.D. soldiers in combat when using nightscopes.