The organ of St Andrew’s Church in Ostönnen, Germany, is, along with the instruments in Sion, Kiedrich and Rysum, one of the oldest organs in the world that are still in playable condition.
The instrument was originally built for the Church of Old St Thomas in nearby Soest. The wood of which the windpipes are constructed suggests a date between 1425 and 1431, and 326 of the pipes seem to have been made before 1500. The first dateable repairs were carried out in 1586 by one Meister Bartholdus, who also installed two new stops. Johann Patroclus Möller was responsible for moving the organ to Ostönnen in 1721–2. Bernhard Dreymann added the 2' superoctave in 1820. In 1888 the traction was reconditioned, and in 1892 the keyboards were renewed. An overhaul was carried out by Paul Ott in 1963, when the organ, apparently mounted over the altar since 1874, was removed to the west wall. Once the value of the instrument had been recognized, the organ builder Rowan West in Altenahr carried out a comprehensive restoration between 2000 and 2003.