The United Opposition (sometimes also called the Joint Opposition) was a group formed in the All-Union Communist Party (Bolsheviks) in 1926 by Leon Trotsky, Lev Kamenev and Grigory Zinoviev in opposition to Joseph Stalin. It demanded, among other things, greater freedom of expression within the Party (in effect, lifting the Ban on Factions imposed by Lenin as a temporary measure in 1921) and less bureaucracy. By this time, Stalin's supporters had already voted Trotsky out from the Politburo.
The grouping was proposed by the Group of 15, a small faction around Vladimir Smirnov which claimed that the Soviet Union was no longer a workers' state. They brought together Trotsky's Left Opposition and Zinoviev's Opposition of 1925. Many former supporters of the Workers Opposition also joined.
Smirnov's group soon left, over differences between themselves and Kamenev and Zinoviev's supporters. Many from Kamenev and Zinoviev's group, as well as most from the Workers Opposition grouping had left by mid-1927, espousing support for Stalin.
In November 1927, the United Opposition held a demonstration in Red Square, Moscow, along with Lenin's widow Krupskaya. However, the Opposition was unable to gain the support of more than a small minority of the party, and were expelled in December 1927 for constituting a faction. Trotsky formed the International Left Opposition with his remaining supporters, and the Group of 15 also continued its opposition. Supporters of these groups were soon exiled or imprisoned, and by 1940, most former supporters of the United Opposition, whether or not they had repudiated it, had been executed on Stalin's orders.
Despite various attempts at rapprochement, the International Left Opposition and the Group of 15 were unable to agree on a further platform.