R31 or R-31 may refer to:
Automobiles Nissan Pintara (R31), a compact car sold in Australia Nissan Skyline (R31), a mid-size car Renault R31, a Formula One racing car
Aviation R31 (airship), of the Royal Navy Renard R.31, a Belgian reconnaissance aircraft Rubik R-31 Dupla, a Hungarian training glider
Other uses R-31 (missile), a Soviet submarine-launched ballistic missile R31 (South Africa), a road Chlorofluoromethane, a refrigerant Herero language , an aircraft carrier of the Royal Navy R31: Contact with acids liberates toxic gas, a risk phrase