The Tajik Soviet Socialist Republic, also commonly known as Soviet Tajikistan, the Tajik SSR, or simply Tajikistan, was one of the constituent republics of the Soviet Union which existed from 1929 to 1991 located in Central Asia.

The Tajik Republic was created on 5 December 1929 as a national entity for the Tajik people within the Soviet Union. It succeeded the Tajik Autonomous Soviet Socialist Republic (Tajik SSR), which had been created on 14 October 1924 as a part of the predominantly Turkic Uzbek SSR in the process of national delimitation in Soviet Central Asia. On 24 August 1990, the Tajik SSR declared sovereignty in its borders. The republic was renamed the Republic of Tajikistan on 31 August 1991 and declared its independence from the disintegrating Soviet Union on 9 September 1991; thus modern Tajikistan is its direct legal successor state.

Geographically, at 143,100 km² (55,300 sq mi), it was bordered by Afghanistan to the south, China to the east, Pakistan to the south, separated by the narrow Wakhan Corridor, as well as internally by fellow Soviet republics of Uzbekistan to the west, Kyrgyzstan to the north.