The Basic Law of the Hong Kong Special Administrative Region of the People's Republic of China, or simply Hong Kong Basic Law, serves as the constitutional document of the Hong Kong Special Administrative Region (HKSAR) of the People's Republic of China (PRC). It was adopted on April 4, 1990 by the Seventh National People's Congress (NPC) of the People's Republic of China, and went into effect on July 1, 1997 replacing the Letters Patent and the Royal Instructions, when this former colony of United Kingdom was handed over to the PRC.

The Basic Law was drafted in accordance with the Sino-British Joint Declaration on the Question of Hong Kong (The Joint Declaration), signed between the Chinese and British governments on December 19, 1984. The Basic Law stipulates the basic policies of the PRC towards the Hong Kong Special Administrative Region. As agreed between the PRC and the United Kingdom in the Joint Declaration, in accordance with the "One Country, Two Systems" principle, socialism as practised in the PRC would not be extended to Hong Kong. Instead, Hong Kong would continue its previous capitalist system and its way of life for a period of 50 years after 1997. A number of freedoms and rights of the Hong Kong residents are also protected under the Basic Law.

The source of authority for the Basic Law is somewhat controversial, with most Chinese legal scholars arguing that the Basic Law is a purely domestic legislation deriving its authority from the Constitution of the People's Republic of China, and with some legal scholars arguing that the Basic Law derives its authority directly from the Sino-British Joint Declaration. The argument is relevant in that it impacts the amount of authority that the PRC has to change the Basic Law, and the ability of the Hong Kong courts to challenge PRC domestic legislation.