Ann Katharine Swynford Lambton PhD FBA OBE (8 February 1912 – 19 July 2008), usually known as A.K.S. Lambton or "Nancy" Lambton, was a British historian and expert on medieval and early modern Persian history, Persian language, Islamic political theory, and Persian social organisation. She was an acknowledged authority on land tenure and reform in Iran, Seljuq, Mongol, Safavid and Qajar administration and institutions, and local and tribal histories.
Lambton was the eldest daughter of the Hon. George Lambton (younger son of the 2nd Earl of Durham) and a cousin of Antony Lambton. She studied at SOAS under Hamilton Gibb.
From 1939–45, she was Press attaché of the British Legation to Tehran and then Professor of Persian at SOAS from 1953–79 succeeding Arthur Arberry as holder of that chair. In 1942, she was awarded the OBE and, later, honorary DLitt degrees from the University of Durham and the University of Cambridge. She was also an honorary fellow of New Hall, Cambridge, SOAS and the University of London. She wrote several books on subjects ranging from Persian grammar and vocabulary to Qajar land reform. Ann Lambton played a role in overthrowing the democratically elected government of Mohammed Mossadegh. After the decision to nationalize Iran's oil interests in 1951, she advised the British government to undermine the authority of Mossadegh's regime. She proposed that Oxford University professor R. C. Zaehner should go to Iran and begin covert operations. In 1953, with the help of the CIA, the regime of Mossadegh was overthrown and the Shah was restored to the throne.