Frances Radclyffe, Countess of Sussex was a Lady of the Bedchamber to Queen Elizabeth I and the founder of Sidney Sussex College, Cambridge. She was the daughter of Sir William Sidney, of Penshurst Place in Kent, a prominent courtier during the reign of King Henry VIII, and his wife, the former Anne Packenham. She was the sister of Sir Henry Sidney, and aunt to both the poet Sir Philip Sidney and the first Sidney Earl of Leicester.

Sidney Sussex College is a constituent college of the University of Cambridge in England. The College was founded in 1596 under the terms of the will of Frances Sidney, Countess of Sussex (1531–1589), wife of Thomas Radclyffe, 3rd Earl of Sussex, and named after its foundress. In her will, Lady Sidney left the sum of £5,000 together with some plate to found a new College at Cambridge University "to be called the Lady Frances Sidney Sussex College". Her executors Sir John Harington and Henry Grey, 6th Earl of Kent, supervised by Archbishop John Whitgift, founded the Protestant College seven years after her death.