The Royal Court Theatre, at different times known as the Court Theatre, the New Chelsea Theatre, and the Belgravia Theatre, is a non-commercial West End theatre on Sloane Square, in the Royal Borough of Kensington and Chelsea, London, England. In 1956 it was acquired by and remains the home of the English Stage Company and is notable for its contributions to contemporary theatre.

The first theatre on Lower George Street, off Sloane Square, was the converted Nonconformist Ranelagh Chapel, opened as a theatre in 1870 under the name The New Chelsea Theatre. Marie Litton became its manager in 1871, hiring Walter Emden to remodel the interior, and it was renamed the Court Theatre.

Several of W. S. Gilbert's early plays were staged here, including Randall's Thumb, Creatures of Impulse (with music by Alberto Randegger), Great Expectations (adapted from the Dickens novel), and On Guard (all in 1871); The Happy Land (1873, with Gilbert Abbott à Beckett; Gilbert's most controversial play); The Wedding March, translated from Un Chapeau de Paille d'Italie by Eugène Marin Labiche (1873); The Blue-Legged Lady, translated from La Dame aux Jambes d'Azur by Labiche and Marc-Michel (1874); and Broken Hearts (1875). By 1878, management of the theatre was shared by John Hare and W. H. Kendal.

Further alterations were made in 1882 by Alexander Peebles, after which its capacity was 728 (including stalls and boxes, dress circle and balcony, amphitheatre, and gallery). After that, Arthur Cecil (who had joined the theatre's company in 1881) was co-manager of the theatre with John Clayton. Among other works, they produced a series of Arthur Wing Pinero's farces, including The Rector, The Magistrate (1885), The Schoolmistress (1886), and Dandy Dick (1887), among others. The theatre closed on 22 July 1887 and was demolished.

The present building was built on the east side of Sloane Square, replacing the earlier building, and opened on 24 September 1888 as the New Court Theatre. Designed by Walter Emden and Bertie Crewe, it is constructed of fine red brick, moulded brick, and a stone facade in free Italianate style. Originally the theatre had a capacity of 841 in the stalls, dress circle, amphitheatre, and a gallery.

Cecil and Clayton yielded management of the theatre to Mrs. John Wood and Arthur Chudleigh in 1887, although Cecil continued acting in their company (and others) until 1895. The first production in the new building was a play by Sydney Grundy titled Mamma, starring Mrs. John Wood and John Hare, with Arthur Cecil and Eric Lewis. By the end of the century, the theatre was again called the "Royal Court Theatre".

Harley Granville-Barker managed the theatre for the first few years of the 20th century, and George Bernard Shaw's plays were produced at the New Court for a period. It ceased to be used as a theatre in 1932, but was used as a cinema from 1935 to 1940, until World War II bomb damage closed it.