The state coat of arms of the Soviet Union (Russian: Государственный герб СССР Gosuarstvennyiy gerb SSSR) was adopted in 1923 and was used until the break-up of the Soviet Union in 1991. Although it technically is an emblem rather than a coat of arms, since it doesn't follow heraldic rules, in Russian it is called герб (transliteration: gerb), the word used for a traditional coat of arms.
The project of the first version of the coat of arms was accepted on July 6, 1923 by the 2nd session of the Central Executive Committee (CIK) of the USSR and the version was completed on September 22 of that year. This design was fixed in the 1924 Soviet Constitution:"The State Emblem of the USSR is composed of a sickle and a hammer on a globe depicted in the rays of the sun and framed by ears of wheat, with the inscription "Workers of All Countries, Unite!" in six languages - Russian, Ukrainian, Belarusian, Georgian, Armenian, Turko-Tatar. At the top of the Emblem is a five-pointed star."
According to the 1936 Soviet Constitution, the USSR consisted of eleven republics. Hence the major new version's difference from the previous one were eleven ribbons bearing USSR State Motto inscriptions in eleven languages.
The number of republics in the USSR became 16 shortly before the Great Patriotic War, but the coat of arms was changed to reflect this only after the war. By a Decision of Presidium of the Supreme Soviet of the USSR of June 26, 1946, all 16 constituent republics were represented on the coat of arms. The USSR State Motto was inscribed on 16 ribbons in 16 languages (Estonian, Latvian, Lithuanian, Moldavian, Finnish languages were added to the previous version). Inscriptions in Azerbaijani, Turkmen, Uzbek, Tajik, Kazakh, Kyrgyz languages were updated due to the transfer from the Latin alphabet to Cyrillic alphabet of respective republics. 
In 1956 Karelo-Finnish SSR was transformed into Karelo-Finnish ASSR and soon this was reflected on the USSR coat of arms. By a Decision of Presidium of the Supreme Soviet of the USSR of September 12, 1956, a ribbon bearing the USSR State Motto in Finnish was removed.
The coat of arms shows the traditional Soviet emblems of the hammer and sickle and the Red Star over a globe, and two wreaths of wheat covered by the USSR State motto ("Workers of the World, Unite!") in the official languages of the Soviet Republics, in the reverse order they were mentioned in the Constitution of the Soviet Union.