Sebastian Fagerlund (born 6 December 1972) is a Finnish composer. He is described as “a post-modern impressionist whose sound landscapes can be heard as ecstatic nature images which, however, are always inner images, landscapes of the mind”. Echoes of Western culture, Asian musical traditions, and heavy metal have all been detected in his music.

His output covers a wide variety of genres, ranging from opera to chamber music and works for solo instruments. The most prominent are his concertos and his works for orchestra.

From 2013-2019 Fagerlund was the artistic director of the RUSK Chamber Music Festival together with clarinetist Christoffer Sundqvist.

Fagerlund was the Composer in Residence of the Royal Concertgebouw in Amsterdam for the 2016-17 season and in 2018 was the invited guest composer at the Aspen Music Festival. In the 2021-22 season, Fagerlund was Artist in Residence at the Tapiola Sinfonietta.