The Sino-British Joint Declaration, formally known as the Joint Declaration of the Government of the United Kingdom of Great Britain and Northern Ireland and the Government of the People's Republic of China on the Question of Hong Kong, was signed by the Prime Ministers of the People's Republic of China (PRC) and the United Kingdom (UK) governments on December 19, 1984 in Beijing.

The Declaration entered into force with the exchange of instruments of ratification on May 27, 1985, and was registered by the PRC and UK governments at the United Nations on June 12, 1985. In the Joint Declaration, the PRC Government stated that it had decided to resume the exercise of sovereignty over Hong Kong (including Hong Kong Island, Kowloon, and the New Territories) with effect from July 1, 1997, and the UK Government declared that it would hand over Hong Kong to the PRC with effect from July 1, 1997. The PRC Government also declared its basic policies regarding Hong Kong in the document.

In accordance with the "One Country, Two Systems" Principle agreed between the UK and the PRC, the socialist system of PRC would not be practiced in the Hong Kong Special Administrative Region (HKSAR), and Hong Kong's previous capitalist system and its way of life would remain unchanged for a period of 50 years. The Joint Declaration provides that these basic policies should be stipulated in the Hong Kong Basic Law.