苏联的加盟共和国，全称是苏维埃社会主义共和国（俄语：Советская Социалистическая Республика）是苏维埃社会主义共和国联盟的组成国家，亦可视为苏联的一级行政区划。1991年苏联解体后，当时的十五个共和国已全部独立成为联合国会员国。

^a 1940年对波罗的海国家的占领为今这些国家的政府及一些西方国家（包括美国和欧盟）认为是非法的。苏联认为这一行动合法，但在1991年9月6日（其解体三个月前）承认其独立地位。

The Republics of the Soviet Union or the Union Republics (Russian:союзные республики, soyuznye respubliki) of the Soviet Union were ethnically based administrative units that were subordinated directly to the Government of the Soviet Union. For most of its history, the Soviet Union was a highly centralized state; the decentralization reforms during the era of Perestroika ("Restructuring") and Glasnost ("Openness") conducted by Mikhail Gorbachev led to the dissolution of the Soviet Union in 1991.