South Yemen (Arabic: اليمن الجنوبي, romanized: al-Yaman al-Janubiyy), officially the People's Democratic Republic of Yemen (جمهورية اليمن الديمقراطية الشعبية, Jumhūriyat al-Yaman al-Dīmuqrāṭīyah al-Sha'bīyah), also referred to as Democratic Yemen (اليمن الديمقراطي, al-Yaman al-Dīmuqrāṭīyy) or Yemen (Aden) (اليمن (عدن), al-Yaman ('Adin)), was a communist state that existed from 1967 to 1990 as a state in the Middle East in the southern and eastern provinces of the present-day Republic of Yemen, including the island of Socotra.

South Yemen's origins can be traced to 1874 with the creation of the British Colony of Aden and the Aden Protectorate, which consisted of two-thirds of the present-day Yemen. Prior to 1937 what was to become the Colony of Aden had been governed as a part of British India, originally as the Aden Settlement subordinate to the Bombay Presidency and then as a Chief Commissioner's province. After the collapse of Aden Protectorate, a state of emergency was declared in 1963, when the National Liberation Front (NLF) and the Front for the Liberation of Occupied South Yemen (FLOSY) rebelled against the British rule.

The Federation of South Arabia and the Protectorate of South Arabia merged to become the People's Republic of Yemen on 30 November 1967, which later changed its name to the People's Democratic Republic of Yemen. It became a Marxist–Leninist one-party state in 1969 and was supported by Cuba, East Germany, North Korea and the Soviet Union. It was the only communist state to be established in the Arab world. Despite its efforts to bring stability into the region, it was involved in a brief civil war in 1986. Following the collapse of the USSR, South Yemen was unified with the Yemen Arab Republic, commonly known as "North Yemen", on 22 May 1990 to form the present-day Republic of Yemen. After three years, however, a political crisis arose between the South's YSP and the North's GPC and Islah parties after the parliamentary elections in 1993. South Yemen declared its secession from the North Yemen in 1994 as the Democratic Republic of Yemen. This effort ended after North Yemen occupied the area as a result of the 1994 civil war. Another attempt to restore South Yemen as a nation, with the Southern Transitional Council as its new government, began in 2017 as part of the 2014 Yemeni Civil War.