Martijn Spierenburg (born 30 January 1975) is a composer and arranger. He is also keyboard player for the Dutch symphonic rock band Within Temptation.
Spierenburg has written and arranged music for several (international) artists, TV series and games. He joined Within Temptation in 2001, shortly after the release of Within Temptation's second full-length studio album, Mother Earth.
Spierenburg co-wrote songs for various Within Temptation albums, including "Angels", "Memories", "Jillian (I'd Give My Heart)", "Our Solemn Hour", "The Cross", "Sinéad" and "Forgiven". He uses Roland keyboards on stage.
Spierenburg also writes orchestral arrangements for the band, and oversees the orchestra when the band are recording albums.