The Sino-British Joint Declaration was a pivotal agreement between China and the United Kingdom that negotiated the terms for the transfer of sovereignty over Hong Kong. Signed in Beijing by Chinese leader Deng Xiaoping and British Prime Minister Margaret Thatcher, the declaration marked the culmination of negotiations that aimed to address concerns regarding the future of Hong Kong after the expiration of British rule in 1997. The agreement stipulated that the British would transfer sovereignty to China while allowing Hong Kong to retain a degree of autonomy under a principle known as 'one country, two systems.' This meant that Hong Kong would maintain its own legal and economic systems, distinct from those of mainland China, for a period of 50 years, until 2047.

The negotiations were influenced by both sides' interests; while the United Kingdom sought to protect the political and economic freedoms of Hong Kong residents, China was eager to reassert its sovereignty over the territory, which had been ceded to Britain in perpetuity following the Opium Wars. The document was significant not only as a diplomatic agreement but also as a symbol of the changing geopolitical landscape in Asia as China began to open up its economy and engage more actively on the global stage. The signing took place amidst broader international scrutiny and was seen as a milestone in Sino-British relations.

Following the signing, the Joint Declaration was registered with the United Nations, reinforcing its international significance. It set the framework for Hong Kong's transition and became a critical part of the region's identity as a Special Administrative Region of China post-1997. This transition period also fostered negotiations about representation, rights, and governance, making it central to discussions on democracy and governance in Hong Kong in the decades that followed.