Julius Martov or L. Martov (Ма́ртов, real name Yuli Osipovich Zederbaum (Russian Ю́лий О́сипович Цедерба́ум)) (November 24, 1873 – April 4, 1923) was born in Istanbul in 1873. The son of Jewish middle class parents, he became the leader of the Mensheviks in early twentieth century Russia.

Forced to leave Russia and with other radical political figures living in exile, Martov joined the Russian Social Democratic Labour Party (RSDLP). At the Second Congress of the RSDLP in London in 1903, there was a dispute between Martov and Vladimir Lenin over who was to be considered a member of the RSDLP. Lenin had published his ideas for moving the party forward in his pamphlet What is to be Done?, which was considered to be a document putting forward the views of the entire Iskra group led by Lenin and Martov. However, in the London Congress of the party differing definitions of party membership were put forward by the two men, with Lenin arguing for a restricted membership of fully committed cadre while Martov argued for a looser interpretation of membership.

Both Martov and Lenin based their ideas for party organization on those prevailing in the European Social Democratic parties in particular that of Germany. When the vote was taken on the disputed question, the group led by Lenin lost and split. However, they were referred to as Bolsheviks throughout the Congress and subsequently as they had won a vote to determine the composition of the Iskra editorial board, hence their adoption of the name Bolshevik which literally means 'person of the majority'. The minority or Menshevik faction adopted that title. Ironically, the vote on the editorial board was not seen as important by any of the disputants at the time, and in fact the Bolsheviks were generally in a minority but some delegates had not been present for the crucial vote who would otherwise have voted for the Mensheviks.

Martov became one of the outstanding Menshevik leaders along with George Plekhanov, Fedor Dan and Irakli Tsereteli. Leon Trotsky too was a member of the Menshevik faction for a brief period but soon broke with them.

After the reforms brought about by the 1905 Revolution, Martov argued that it was the role of revolutionaries to provide a militant opposition to the new bourgeois government. He advocated the joining a network of organisations such as trade unions, cooperatives, village councils and soviets to harass the bourgeois government until the economic and social conditions made it possible for a socialist revolution to take place.

Martov was always to be found on the left wing of the Menshevik faction and supported the reunification with the Bolsheviks in 1905. That fragile unity was short lived, however, and by 1907 the two factions had again split in two.

In 1914 Martov was a part of the opposition to the First World War, which he viewed as an imperialist war in terms very similar to those of Lenin and Trotsky. He therefore became the central leader of the Menshevik Internationalist faction which organised in opposition to the Menshevik Party leadership.

After the February Revolution in 1917, Martov returned to Russia but was too late to stop some Mensheviks joining the Provisional Government. He strongly criticized those Mensheviks such as Irakli Tsereteli and Fedor Dan who, now part of Russia's government, supported the war effort. However, at a conference held on June 18, 1917, he failed to gain the support of the delegates for a policy of immediate peace negotiations with the Central Powers.

When the Bolsheviks came to power as a result of the October Revolution in 1917, Martov became politically marginalised, best exempified by Trotsky's comment to him and other party members as they left the first meeting of the council of Soviets after October 25th 1917 in disgust at the way in which the Bolsheviks had seized political power, "You are pitiful isolated individuals; you are bankrupts; your role is played out. Go where you belong from now on — into the dustbin of history!". Martov silently walked away without looking back. He paused at the exit seeing a young Bolshevik worker wearing a black shirt with a broad leather belt, standing in the shadow of the portico. The young man turned on Martov with unconcealed bitterness: 'And we amongst ourselves had thought, Martov would at least will remain with us.' Martov stopped and with a characteristic movement tossed up his head to emphasize his reply: 'One day you will understand the crime in which you are taking part,'. Waving his hand wearily he left the hall.

For a while Martov led the small Menshevik opposition group in the Constituent Assembly until the Bolsheviks abolished it. On one occasion a factory section chose Martov as their delegate ahead of Lenin in a soviet election. Shortly afterwards the factory found its supplies reduced.

The Mensheviks were banned along with other political parties (except for the Communists) by the Soviet government during the Russian Civil War.

Martov supported the Red Army against the White Army during the Civil War; however, he continued to denounce the persecution of liberal newspapers, the Cadets and the Socialist-Revolutionaries.

In 1923 Martov was forced into exile and he died in Schömberg, Germany the same year. Before dying, however, he was able to launch the newspaper Socialist Messenger which remained the publication of the Mensheviks in exile in Berlin, Paris and eventually in New York when the last of them passed. It has been rumored that Lenin, also on his deathbed at the time, provided funds for this last venture of Martov.