Invitation to the Castle (French: L'Invitation au château) is a 1947 satirical play by the French playwright Jean Anouilh. It was adapted in 1950 by Christopher Fry as Ring Round the Moon. The play concerns twins, a cold, manipulative playboy Hugo, and his sensitive brother Frédéric. Frédéric is madly in love with Diana, the spoiled daughter of a self-made millionaire. She herself wants Hugo, as his impenetrability teases her. To show to Frédéric that Diana is not worth his attentions, Hugo invites to a ball Isabelle, a lower-class dancer, whom he Pygmalion-like transforms into an aristocratic beauty.

The play was first presented on 5 November 1947 at the Théâtre de l'Atelier, Paris. The production was directed by Peter Brook. The first production on Broadway, in 1950, starred Denholm Elliott and Stella Andrew.

The French composer Francis Poulenc wrote a chamber suite on Invitation to the Castle.