Betrothal in a Monastery (original Russian title Обручение в монастыре), Op. 86 is an opera by Sergei Prokofiev, his sixth with an opus number. The libretto, in Russian, was by the composer and Mira Mendelson (his companion in later life), after Richard Brinsley Sheridan's ballad opera libretto for Thomas Linley the younger's The Duenna.

Prokofiev began the work in 1940, and it was in rehearsal that year, but World War II halted production of the opera. The first performance did not occur until 3 November 1946 at the Kirov Theatre with Boris Khaikin conducting.

Commentators have noted that, given the context of its creation in the 1940s in the Soviet Union, this opera lacks any particular political or social comment, except perhaps for a scene involving drunken monks.

In recent years, the opera has been performed in 1989 at the Wexford Festival, in 2006 at the Glyndebourne Festival and at the Palau de les Arts in Valencia, Spain in 2008.