Rieger Orgelbau is an Austrian firm of organ builders, known generally as Rieger. The firm was founded by Franz Rieger. From 1873 it was known as Rieger & Söhne, and from 1879 as Gebrüder Rieger, after his sons took over. At the end of World War II, the firm was nationalised by the Czech government and merged with another workshop as Rieger-Kloss. The Rieger tradition was also continued by the owners and workers of the original firm, who moved to Austria and founded a new workshop as "Rieger Orgelbau".