Monna Vanna (Russian: Монна Ванна) is an unfinished opera by Sergei Rachmaninoff after a play by Maurice Maeterlinck.

Rachmaninoff had completed Act I in short vocal score, with piano accompaniment, and then he went to ask for permission to set the text in a full three-act treatment.

This opera could only have been produced in countries that at the time were not signatories to European copyright law, such as Russia.

Ultimately, Rachmaninoff abandoned further work on this opera and never wrote a complete setting.

[1] Years later, at the request of Sophie Satin, Rachmaninoff's sister-in-law,[2] Igor Buketoff prepared a performing orchestrated edition of Act I, which he conducted in its world premiere with the Philadelphia Orchestra on 11 August 1984 at Saratoga Springs, New York with Tatiana Troyanos in the title role, Sherrill Milnes as Guido, and John Alexander as Guido's father.