Ein Walzertraum (A Waltz Dream) is an operetta by Oscar Straus with a German libretto by Leopold Jacobson and Felix Dörmann, based on the novella Nux, der Prinzgemahl (Nux, the Prince Consort) by Hans Müller-Einigen from his 1905 book Buch der Abenteuer (Book of Adventures).
The young Jacobson presented Straus with a libretto for Ein Walzertraum at a coffee house in the Vienna Prater in 1906. Straus was inspired by the text and completed the work within 12 months for its premiere in spring 1907.