Janne Reidar Stefansson (born 19 March 1935) is a retired Swedish cross-country skier.
He competed at the 1960 and 1964 Olympics in the 15 km and 4×10 km events and won a gold medal in the relay in 1964, finishing fourth in 1960.
He also finished fourth-fifth in the 15, 30 and 50 km events in 1964.Stefansson won a silver over 30 km at the 1962 FIS Nordic World Ski Championships in Zakopane.
He also won the long distance cross-country ski race Vasaloppet on seven occasions between 1962 and 1969, only missing victory in 1967, when he finished second behind Assar Rönnlund.