Die Göttin der Vernunft (The Goddess of Reason) was the last completed operetta of Johann Strauss II. It was written to a libretto by A. M. Willner and Bernhard Buchbinder and was first performed at the Theater an der Wien on 13 March 1897.

The creation of the opera was announced in a Vienna newspaper in July 1896, which reported that Strauss had commenced work on the opera with Willner and Buchbinder, intending to produce it in the autumn of 1897. However, as the composer gradually received the text of the libretto over the ensuing months, he began to dislike the scenario, which made light of the violence of the French Revolution. He tried to discontinue his work, but this would have made him liable to an action for breach of contract from the librettists, and he therefore reluctantly carried on, with Willner writing to him "On the day after the première, you will see how wrong you have been." Strauss did not attend the première, claiming a bronchial infection—the only one of his works where he was not present on the opening night—and he was informed of the work's reception during the evening by telephone.^[1] However, Strauss's admirer Johannes Brahms was in the audience, his last public appearance before his death in April.^[2] The reception of the work by audience and press was not unfavourable, although one newspaper asked "can one disguise a blood-red guillotine with flowers?" During the run of 36 performances, a number of cuts were made, Strauss providing an overture only by the 25th performance.^[1]

The opera was subsequently never revived in its original form. In 1909, ten years after the composer's death, the music was adapted to an entirely new libretto and presented as Reiche Mädchen (Rich Girls).^[1] The music and libretto had by now been separated by legal process, so Willner reworked the story-line of the libretto as Der Graf von Luxemburg (The Count of Luxembourg) for Franz Lehár.^[3]

The conductor Christian Pollack recreated Strauss's original version from manuscripts in the Austrian National Library and in 2009 staged the first revival of the opera since its première in Žilina, Slovakia.^[1]

The opera takes place in the town of Châlons in 1794, during the Reign of Terror of the French Revolution. It is centred on the plans of Robespierre to replace Christianity with a state religion worshipping the Goddess of Reason. These plans involved public displays of the "Goddess" that were organised by activists such as Pierre Gaspard Chaumette, who stage managed a partly unclothed Goddess entering in procession to Notre Dame cathedral and arranged similar proceedings across the country.^[1]