Isidore was the son of a merchant, who became a chemist's assistant. In 1898, he started participating in the Group of Workers Revolutionaries. He a later became a member of the Menshevik faction ofthe RSDLP. He was imprisoned for inciting the Izhorskiye workers to strike. In 1904 he went to Baku, and used the name Theodor Izmaylovich for his political work. By 1906 he was secretary of the newspaper New Life. He then went to Odessa before travelling abroad. In 1907, he returned to Russia, was arrested, again brought totrial but acquitted (1908). He settled in Moscow. After the February Revolution of 1917, he was appointed treasurer of the PK Russian Social Democratic Workers' Party (Bolsheviks). After the October Revolu- tion, he worked as Deputy People's Commissar of Finance, on March 2, 1918 he hea- ded the Oil Commissariat, and on March 21, 1918, he was simultaneously appointed People's Commissar of Finance of the RSFSR (until August 16, 1918). In April 1918, he proposed a set of measures close to what was later called the "New Economic Policy"; under his influence, Lenin radically changed the content of the original version of the article "The Immediate Tasks of Soviet Power". Member ofthe All-Russian Central Executive Committee (1918-1919), mem- ber of the collegium of the People's Commissariat of State Control (since 1920, the RCI of the RSFSR, 1919-1921).