Hong Kong Foundation Day (Chinese: 香港開埠日), also known as Hong Kong Day (香港日) and Festival of Hong Kong (香港節), is the anniversary of the founding of Hong Kong as a free port when Britain formally colonised it on 26 January 1841 after entering into a provisional treaty, known as the Chuenpi Convention, with an official of the Qing government. The British Colonial Government did not make it an official public holiday, nor does the SAR Government. Yet, some members of the public do organise various history talks or exhibitions on or near 26 January each year.

Hong Kongers, most being native speakers of Cantonese, call this day 開埠日 or hōi fauh yaht, which means “the day of pier opening”, reflecting the original intention of the British acquisition of Hong Kong was for opening it up and turning it into a port of free trade. The name also signifies that international commerce became legally permitted in Hong Kong upon British administration whereas Hong Kong had not been allowed to conduct foreign trade under the Canton System policy of the Qing government.

In January 1841, after a series of negotiations, a provisional treaty seeking to end the First Opium War between Britain and the Qing Dynasty, known as the Convention of Chuenpi, was struck by representatives from the two sides, namely, Plenipotentiary Charles Elliot and Imperial Commissioner Qishan. With the instruction given to him to take possession of some islands for trade in the previous year, Elliot demanded and secured the cession of Hong Kong Island as one of the terms of the Convention even though Zhoushan Island had been preferred by his boss Lord Palmerston. While in Macau, Elliot announced the details of the Convention by publishing a circular on the 20th.

Four days after the announcement, Captain Edward Belcher, aboard HMS Sulphur, surveyed Hong Kong Island and landed the next morning on the 25th at 8:15 o'clock, but he did not proceed to take formal possession of it. Yet, he did claim themselves being the bona fide first possessors, and they drank to the Queen's health with three cheers.

In addition, some merchants rushed from Macau to Hong Kong Island for the upcoming ceremony after learning the news in Macau.

In the end, a formal possession ceremony was held on 26 January by Commodore Gordon Bremer at Possession Point. He was accompanied by other officers of the squadron. The Royal Marines fired a feu de joie, and the war ships performed a Royal Salute. The Union Jack was hoisted before the crowd, symbolising the beginning of British rule.

Today, news media often have history quizzes ready for their audiences on Foundation Day, and non-governmental organisations arrange history talks and exhibitions for the general public to participate.

But celebrations are not limited to Hong Kong. Events have been held in overseas metropolises with significant numbers of diaspora Hong Kongers, such as London and Melbourne. Hong Kong street food stalls, mini-concerts featuring Hong Kong music, and other cultural activities can also be found in these overseas events in addition to history-focused exhibitions and talks.