Blithe Spirit is a comic play by Noël Coward, described by the author as "an improbable farce in three acts". The play concerns the socialite and novelist Charles Condomine, who invites the eccentric medium and clairvoyant Madame Arcati to his house to conduct a séance, hoping to gather material for his next book. The scheme backfires when he is haunted by the ghost of his wilful and temperamental first wife, Elvira, after the séance. Elvira makes continual attempts to disrupt Charles's marriage to his second wife, Ruth, who cannot see or hear the ghost.

The play was first seen in the West End in 1941 and ran for 1,997 performances, a new record for a non-musical play in London. It also did well on Broadway later that year, running for 657 performances. The play was adapted for the cinema in 1945; a second film version followed in 2020. Coward directed a musical adaptation, High Spirits, seen on Broadway and in the West End in 1964. Radio and television presentations of the play have been broadcast in Britain and the US from 1944 onwards. It continues to be revived in the West End, on Broadway and elsewhere.

The title of the play is taken from Shelley's poem "To a Skylark", ("Hail to thee, blithe Spirit! / Bird thou never wert"). For some time before 1941 Coward had been thinking of a comedy about ghosts. His first thoughts centred on an old house in Paris, haunted by spectres from different centuries, with the comedy arising from their conflicting attitudes, but he could not get the plot to work in his mind. He knew that in wartime Britain, with death a constant presence, there would be some objection to a comedy about ghosts, but his firm view was that as the story would be thoroughly heartless, "you can't sympathise with any of them. If there was a heart it would be a sad story."

After his London office and flat had been destroyed in the Blitz, Coward took a short holiday with the actress Joyce Carey at Portmeirion on the coast of Snowdonia in Wales. She was writing a play about Keats, and he was still thinking about his ghostly light comedy. He later recounted:

We sat on the beach with our backs against the sea wall and discussed my idea exclusively for several hours. Keats, I regret to say, was not referred to. By lunchtime the title had emerged together with the names of the characters, and a rough, very rough, outline of the plot. At seven-thirty the next morning I sat, with the usual nervous palpitations, at my typewriter. ... I fixed the paper into the machine and started. Blithe Spirit. A Light Comedy in Three Acts. For six days I worked from eight to one each morning and from two to seven each afternoon. On Friday evening, May ninth, the play was finished and, disdaining archness and false modesty, I will admit that I knew it was witty, I knew it was well constructed, and I also knew that it would be a success.

Charles Condomine is a successful novelist. At the start of the play, while dressing for dinner, he and his second wife, Ruth, discuss his first wife, Elvira, who died young, seven years earlier. He comments, "I remember her physical attractiveness, which was tremendous, and her spiritual integrity, which was nil". Among the Condomines' dinner guests is an eccentric medium, Madame Arcati, whom Charles has invited in the hope of learning about the occult for a story he is writing. He has arranged for her to conduct a séance after dinner. During the séance she plays a recording of Irving Berlin's song "Always" on the gramophone, inadvertently attracting the ghost of Elvira.

The medium leaves, unaware of what she has done. Only Charles can see or hear Elvira, and Ruth does not believe that Elvira exists, until a floating vase is handed to her out of thin air. The ghostly Elvira makes continued, and increasingly desperate, efforts to disrupt Charles's current marriage. Charles accuses her of being "feckless and irresponsible and morally unstable". She finally sabotages his car in the hope of killing him so that he will join her in the spirit world, but it is Ruth rather than Charles who drives off and is killed.

Ruth's ghost immediately comes back for revenge on Elvira, and though Charles cannot at first see Ruth, he can see that Elvira is being chased and tormented, and his house is in uproar. He calls Madame Arcati back to exorcise both the spirits, but instead of banishing them she unintentionally materialises Ruth. With both his dead wives now fully visible, and neither of them in the best of tempers, Charles, together with Madame Arcati, goes through séance after séance and spell after spell to try to exorcise them. It is not until Madame Arcati works out that the housemaid, Edith, is psychic and had unwittingly been the conduit through which Elvira was summoned that she succeeds in dematerialising both ghosts. Charles is left seemingly in peace, but Madame Arcati, hinting that the ghosts may still be around unseen, warns him that he should go far away as soon as possible. Coward repeats one of his signature theatrical devices at the end of the play, where the central character tiptoes out as the curtain falls – a device that he also used in Present Laughter, Private Lives and Hay Fever. Charles bids his vanished wives farewell and leaves at once; the unseen ghosts throw things and wreck the room as soon as he has gone.