R3

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

Aviation

 * Aviatik R.III, a German aircraft
 * DFW R.III, a World War I German bomber aircraft
 * Ross R-3 glider
 * Tupolev R-3 Soviet reconnaissance aircraft
 * Yakutia Airlines IATA airline designator

Entertainment

 * 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

Military

 * 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

Math and Science

 * 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

Transportation

 * 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

Other uses

 * 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