"Baynard's Castle" was at various times a castle, house and palace that existed on the same site, in the south west corner of the City of London, for 600 years from the time of the Norman Conquest until the Great Fire of London. It had a strategic position on the bank of the Thames where the city walls came down to the river, by the River Fleet and the Fleet Tower (near the present day Blackfriars Station).

Although nothing of the building remains, it can be seen in old views of London, and the name survives as Castle Baynard Street, just south of Queen Victoria Street.

Part of William Shakespeare's play Richard III takes place in Baynard Castle.