R3

R3, R.III or R-3 or R/3 may refer to:

Aviation[edit]

BBC Radio 3, a radio operated by the BBC within the United Kingdom
R3 (TV series), produced by the BBC between 1964 and 1965
Region 3, the DVD region code for Southeast Asia, South Korea, Republic of China (Taiwan), Hong Kong, Macau
Resistance 3, the third game in the Resistance series
R3 (video game), a computer game for the Amiga series of computers in 1995

Version of the German Rheintochter ground to air missile
R-3 (missile), an abandoned Soviet ICBM design from the late '40s.
K-13 (missile), the Vympel K-13, an air-to-air missile also known as R-3S in Soviet service
R-3 tank, a proposed Romanian tank design for use in World War II
USS R-3, a 1919 R-class coastal and harbor defense submarine of the United States Navy

R3: Extreme risk of explosion by shock, friction, fire or other sources of ignition, a risk phrase in chemistry
R-3 process, a chromogenic photo process for making Type R prints
R3 or receptor 3, the third in line of a series of cellular receptors, generally at the end of an acronym
R³, three-dimensional space, the Euclidean space of real numbers in three dimensions

R3 expressway (Czech Republic), a road connecting Kaplice and the border with Austria
R3 expressway (Slovakia), a road connecting Krupina and Zvolen
R3 (RER Vaud), an S-Bahn line in the canton of Vaud
Radial Road 3 or R-3, an arterial road of Manila, Philippines
R-3 motorway (Spain), a road connecting Madrid and Tarancón
R3 (SEPTA), a former commuter rail line in and near Philadelphia, Pennsylvania, which has been split into:
- Media/Wawa Line (R3 Media/Elwyn, formerly R3 West Chester),
- West Trenton Line (SEPTA) (R3 West Trenton)
R3 (ring road) in Belgium
R3 (Rodalies de Catalunya), a commuter rail line in Barcelona, Catalonia, Spain
R3 Lougheed Hwy, an express bus route in Metro Vancouver, British Columbia, Canada
R3 road (Zimbabwe), a road connecting Chirundu with Harare

Ågesta Nuclear Plant, also known as R3, was the third nuclear reactor built in Sweden
Jaguar R3, a car made by Jaguar Racing for the 2002 Formula One season
Leica R3, a 1976 35mm SLR camera
Reduce, reuse, recycle
SAP R/3, the previous designation for an enterprise resource planning software produced by SAP AG; the new name is SAP ERP
Yamaha YZF-R3
ISO Recommendation R3, a forerunner to the international standard ISO 3
Canon EOS R3, a Canon full-frame mirrorless interchangeable-lens camera