Orgeln des Stephansdoms, Pipe organ in St. Stephen's Cathedral, Vienna, Austria

St. Stephen's Cathedral holds four organs. The Riesen-Orgel stands on the west gallery above the Riesentor, a Romanesque funnel portal; Rieger built it in 2017–2020, reusing the 1960 Kauffmann organ's pipes and its angel-bearing prospectus carved by Josef Troyer. A second Rieger organ (1991, 54 stops) stands in the right aisle, and the mobile Haydn-Orgel (2009, 12 stops) is kept for concerts.

An organ at St. Stephen's is first documented in 1334 and repaired by the organist Peter in 1371. Anton Pilgram completed the Orgelfuß in 1513, and Hermann Raphael Rodensteen built a new instrument there in 1566–1567. In 1797 the side-aisle organs were dismantled and their pipes reused in a larger west-gallery organ, later rebuilt by Walcker in 1886 and destroyed in the April 1945 fire.

The name Riesenorgel for the west-gallery instrument comes from its position above the Riesentor, the Romanesque funnel portal. Since 2009 the cathedral has a mobile Haydn-Orgel, built by Rieger for the bicentenary of Joseph Haydn's death. The 2020 consecration was marked by a concert of the cathedral organists Konstantin Reymaier and Ernst Wally, followed by a festival running to 26 October.

The best way to hear the organ is during regular concerts and church services when it fills the entire interior space with its sound. Visitors should check current scheduling beforehand since performances vary depending on the season and special events at the cathedral.

The 1960 Kauffmann organ had 125 stops and about 10,000 pipes, then the largest organ ever built in Austria. Its angels carrying the free pipe facade were carved by the East Tyrolean sculptor Josef Troyer. Since 2017 Rieger has rebuilt the instrument, keeping the facade and 42% of the Kauffmann pipes; it was consecrated on 4 October 2020.