Ernst Reijseger (born 13 November 1954) is a Dutch cellist and composer. He specializes in jazz, improvised music, contemporary classical music and often gives solo concerts. He has worked with Louis Sclavis, Derek Bailey, Han Bennink, Misha Mengelberg, Gerry Hemingway, Yo-Yo Ma, Albert Mangelsdorff, Franco D'Andrea, Joëlle Léandre, Georg Gräwe, Trilok Gurtu, and Mola Sylla, and has done several world music projects working with musicians from Sardinia, Turkey, Iran, Senegal, and Argentina, as well as the Netherlands-based group Boi Akih.
He has made numerous recordings, both as solo cellist and with other groups, and has been the subject of a documentary film. He has also written several film scores, including scores for a number of Werner Herzog films.