The country's name comes from a combination of Tanganyika, which is the large mainland territory, and Zanzibar, the offshore archipelago. The two former British colonies united in 1964, forming the United Republic of Tanganyika and Zanzibar. Later the same year the country was renamed the United Republic of Tanzania.

Tanzania as it exists today consists of the union of what was once Tanganyika and the islands of Zanzibar. Formerly a German colony from the 1880s through 1919, the post-World War 1 accords and the League of Nations charter designated the area a British Mandate (except for a small area in the northwest, which was ceded to Belgium and later became Rwanda and Burundi).

After the leftist Zanzibar Revolution overthrowing the Sultan in neighboring Zanzibar, which had become independent in 1963, the island merged with mainland Tanganyika to form the nation of Tanzania on April 26, 1964. The union of the two, hitherto separate, regions was controversial among many Zanzibaris (even those sympathetic to the revolution) but was accepted by both the Nyerere government and the Revolutionary Government of Zanzibar owing to shared political values and goals.

Tanzania has more than 126 ethnic groups and each ethnic group has its own language. No language is de jure official, but Swahili is the de facto national language, used for inter-ethnic communication and for official matters. After gaining independence, English, the language of colonial administration during the era of British rule, was still used for some official issues, and was thus considered de facto national alongside Swahili.

Nowadays English is no longer used in the administration, in the parliament or in the government, so it is no longer a de facto official language in the narrow sense. Hence Tanzania is one of the few African states in which a local language has gained importance to the disadvantage of the ex-colonial language. Since English is still the language of higher courts it can however be considered a de facto official language in the larger sense.

Other spoken languages are Indian languages, especially Gujarati, and Portuguese (both spoken by Mozambican blacks and Goans). Historically German was widely spoken during that colonial period, but few remain alive who remember that period.