The Byelorussian Soviet Socialist Republic (abbreviated as Byelorussian SSR or BSSR) (Belarusian: Беларуская Савецкая Сацыялістычная Рэспубліка [БССР] Belaruskaya Savetskaya Satsyyalistychnaya Respublika [BSSR]; Russian: Белору́сская Сове́тская Социалисти́ческая Респу́блика [БССР] Belorusskaya Sovetskaya Sotsalisticheskaya Respublika [BSSR]) was one of fifteen constituent republics of the Soviet Union. It was one of the four original founding members of the Soviet Union in 1922, together with the Ukrainian SSR, the Transcaucasian SFSR and the Russian SFSR. The Soviet Republic, along with the Ukrainian SSR and the Soviet Union, were founder members of the United Nations Organization in 1945.
The Soviet republic, Socialist Soviet Republic of Byelorussia, in the lands of Belarus was declared on 1 January 1919, but it took a few years to define its status. Byelorussia was also one of several Soviet Republics occupied by Nazi Germany during World War II. The end of the Soviet Republic occurred in 1991 and the country was later renamed into the current Republic of Belarus.