The Union State is a supranational organization, composed of Russia and Belarus since its creation in 1999. It is formally open to membership applications from other countries. Union State members share freedom of migration to work or live in respective countries, have an integrated military, and have policies to promote economic integration and some coordinated tax policies. From 2004 to 2008, there were some negotiations to adopt a common currency, which did not come to pass.

David R. Cameron, writing for the Yale MacMillan Center, suggests the Union State is an attempt to put the USSR back together.

During the buildup to the 2022 Russian Invasion of Ukraine, Belarussian President Alexander Lukashenko predicted in an interview that Ukraine would eventually join the Union State, saying "If you say 15 years, I'm sure that Ukraine will be there if we don't make any mistakes". Ukrainian President Volodymyr Zelensky said in 2021 that a "true Union State" was a real danger to Ukraine.