Tanganyika ( /ˌtæŋɡənˈjiːkə/), from 1962 the Republic of Tanganyika, was a sovereign state in East Africa from 1961 to 1964. It was situated between the Indian Ocean and the African Great Lakes of Lake Victoria, Lake Malawi and Lake Tanganyika. It gained independence from the United Kingdom as a Commonwealth Realm on 9 December 1961, becoming a republic within the Commonwealth of Nations exactly a year later on 9 December 1962. On 26 April 1964, Tanganyika joined with the islands of Zanzibar to form the United Republic of Tanganyika and Zanzibar, a new state that changed its name to the United Republic of Tanzania within a year.

Tanganyika originally consisted of the British share of the former German colony of German East Africa which the British took under a League of Nations Mandate in 1922, later transformed into a United Nations Trust Territory after the World War II. The other parts of German East Africa were taken into Belgian Trusteeship, eventually becoming known as modern day Rwanda and Burundi.