R8 or R-8 may refer to:
- Audi R8, used from 1999–2006 by Audi for Le Mans 24 Hours race cars, and from 2007–2024 for a street legal car
- R8 Machine taper, originally designed for Bridgeport Milling Machines
- R8 (Rodalies de Catalunya), a commuter rail line bypassing Barcelona, Catalonia, Spain
- R8 (SEPTA), a commuter rail line in Philadelphia, United States, which has been split into:
- Chestnut Hill West Line: (R8 Chestnut Hill West)
- Fox Chase Line: (R8 Fox Chase)
- R8 (RER Vaud), an S-Bahn line in the canton of Vaud
- R8: Contact with combustible material may cause fire, a risk phrase in chemistry
- HK R8, a modified version of the Heckler & Koch SL8 rifle
- Smith & Wesson M&P R8, a .357 Magnum revolver
- HP roman8, an 8-bit character set
- Kaliningrad K-8, a medium-range air-to-air missile known as R-8 in service
- Kyrgyzstan Airlines, from its IATA airline designators
- Leica R8, a 1996 manual focus 35 mm single-lens reflex camera
- Canon EOS R8, a mirrorless camera
- Radial Road 8 or R-8, an arterial road of Manila, Philippines
- Receptor 8, the eighth in line of a series of cellular receptors, generally at the end of an acronym
- Renault 8, a small family car produced in the 1960s and early 1970s
- Roland R-8, a 1988 electronic drum machine
- USS R-8 (SS-85), a 1919 United States Navy submarine
- R8, sometimes used as text/SMS speak for "Reyt", a term used in Northern England. (Short for "Alright", or "Alreyt")
- R8A (New York City Subway car)