As an improviser, and from 1977 as leader of his own ensembles, Maarten (van Regteren) Altena (Amsterdam, 22 January 1943) has built an international reputation. He is pioneering a music that manages to structure improvisation with composed elements in an inimitable and sophisticated manner. Over the years writes dozens of compositions for his own ensembles. Together with Michel Waisvisz he founds the Stichting Claxon (Claxon Foundation) in 1978, which releases records as well as organizing five festivals. They are awarded the 1978 Wessel Ilcken Prijs (the major Dutch jazz award at the time) for their work. From 1991 to 2001 Altena is involved in the concert series Rumori. He stops playing the double bass in his own ensemble in 1997, but he continues as artistic director and supplier of compositions. In November 2005 he celebrates his 25th anniversary with the Maarten Altena Ensemble and steps back as its artistic director.