The Sino-British Joint Declaration was signed in 1984 and transferred control of Hong Kong to the People’s Republic of China from 1 July 1997. This set the scene for the establishment of the Special Administrative Region (SAR) in Hong Kong. Lim uses British archival sources to re-examine the Joint Declaration, the negotiations that led up to it and its resounding significance. Beginning with Margaret Thatcher’s preparations for her Beijing trip, his recent book, Treaty for a Lost City: The Sino-British Joint Declaration (Cambridge University Press, 2022) takes a chronological approach. In light of current developments, Lim will set out to explain some of the legal complexities that have underpinned the relationships between China, Hong Kong and Britain since 1979.