An der Moldau is a polka-française by Johann Strauss Sohn (op. 366). The work was performed for the first time on 25 October 1874 in the concert hall of the Vienna Musikverein.
The polka was based on motifs from the operetta Die Fledermaus. The work thus joins a series of compositions (opus numbers 362, 363, 365, 367 and 368) which all take up themes from this operetta. The main theme of the polka comes from the ballet music from the second act of Die Fledermaus. However, this is no longer played in many performances of the operetta today or is replaced by interludes from other works by Strauss or other composers. In the original version, the dance on which this polka is based is based on the text Marianka, komm' und tanz' me hier. However, parts from Act 3 of the operetta are still quoted in the polka, such as the songs Ein seltsam Abenteuer and O Fledermaus, o Fledermaus, laß endlich doch dein Opfer aus.
 
The title of the polka refers to the ballet music mentioned above, which consists of five national dances. Among them is also a Bohemian polka. The title of the polka is derived from the fact that the Vltava flows through Bohemia. Strangely enough, this polka is not listed in the few surviving programmes of the Strauss Orchestra.