Bjørn "Lillebjørn" Falk Nilsen (born 21 December 1950 in Oslo) is a prominent Norwegian singer-songwriter and folk musician. He is also considered somewhat the leading "voice of Oslo" thanks to numerous classic songs about the city from the 1970s and up.
He also makes up the Norwegian supergroup Gitarkameratene with Jan Eggum, Halvdan Sivertsen and Øystein Sunde.
In 1987 he received the Fritt Ord Honorary Award.
Nilsen has collaborated with his friend and idol Pete Seeger on numerous occasions. He adapted Pete Seeger's song My Rainbow Race into Norwegian as Barn av regnbuen ("Children of the Rainbow"). Anders Behring Breivik said that he hated that song, and saw it as a symbol of "cultural Marxism" and multiculturalism. In response, on 26 April 2012, over 40,000 Norwegians sang it publicly outside his trial.