F4, F.IV, F04, F 4, F.4 or F-4 may refer to:
- F4 (Istanbul Metro), a funicular railway in Istanbul Turkey
- F4 Cross Harbour, or Cross Harbour ferry services (2017–2020), Sydney, Australia
- F4 Pyrmont Bay, or Pyrmont Bay ferry services, Sydney, Australia
- Albarka Air (IATA code), a Nigerian airline
- Front-engine, four-wheel-drive layout, in automotive design
- MV Agusta F4 series, a series of motorcycles
- USS F-4, a U.S. Navy submarine that sank near Honolulu harbor in 1915
- LNER Class F4, a class of British steam locomotives
- F4, a paper size
- F 4 Frösön, a former Swedish Air Force wing
- f/4, an f-number of an optical system such as a camera lens
- F-4 Object, or Rákosi bunker, a formerly secret nuclear shelter in Budapest, Hungary
- Form F-4, an American form used to register securities
- Nikon F4, a camera
- F4, a tornado intensity rating on the Fujita scale
- F4, an electrode site according to the 10–20 system (EEG)