The article analyzes the process of genesis of the left flank of the Russian party system in the spring – summer of 1917. The outbreak of the Russian Revolution completely destroyed the old system of political parties based on Duma activity and Duma elections. There were two tendencies in the development of the Russian Social democratic movement – towards consolidation, unification into a single party and towards a split, the formation of a number of independent parties. By the autumn of 1917, the Social Democrats, separating and uniting, took shape into two opposing all-Russian parties – the RSDLP (united) and the RSDLP (Bolsheviks), as well as the RSDLP (internationalists), which took an intermediate position between them, and a number of small organizations, mainly national.

The article continues the analysis of the transformation of the left flank of the Russian party system in the autumn of 1917. At that time, the former leaders of the political process – the Mensheviks and Social Revolutionaries – gradually lost their positions, and in October they were completely removed from power, and they were replaced by the Bolsheviks and left Social Revolutionaries. Attempts to create a broader government coalition ended in the failure of negotiations under Vikzhel, and the dispersal of the Constituent Assembly further deepened the split between the Socialists.

The article continues the analysis of the transformation of the left flank of the Russian party system in the spring of 1918. After the dispersal of the Constituent Assembly, the government bloc of Bolsheviks and left SRS took shape and the division among the Social Democrats deepened even more. The Bolsheviks increasingly opposed themselves to them, adopting the name of Communists. Their alliance with the left srs proved to be short-lived. The RCP(b) formed a one-party government.

The authors runs back the process of political parties genesis in the Russian empire, defines the chronological limits of the process and its stages. The author shows that Russia had a rich experience of political struggle rooted in the very ancient times and supposes that it is inaccurate to maintain that the genesis of Russian parties considerably lagged behind the similar process in the West. The thesis that parties emerged first in the national periphery of the empire is also incorrect. On the contrary, it was the national center (and the imperial capital) that gave examples of party building. Socialist organizations that at the early stages of genesis outraced conservative and liberal formations by pace of development, yet finally completed their emergence later than liberal and conservative parties. That corresponds with the world practice. Having selected formed parties according the characteristics stipulated in the article the author obtains data on parties' memberships that are more modest than data usually mentioned in the historic literature. The selected parties are classified according to territorial-national and doctrinal criteria.

The author tracks the development of conceptual basis of the Russian empire’s political parties study. Over the past 15 years an impressive progress in study of the Russian political parties has been achieved: full scale serial publication is going on, monographs dedicated to individual parties have been written, and several general works that allow characterize the system of political parties have been published. However understanding of enormous volume of accumulated material is impeded by an inadequate attention to methodological issues. On one hand, historians and specialists in history of parties perform their studies in insulation from each other. Interdisciplinary studies are the pressing need. On the other hand, conceptual results produced by the Russian scientists and political figures of the early 20th century are left behind though these results deserve attention and scrutiny.

The published text is the first public appearance of the prominent Russia Social Democrat, one of the Mensheviks' leaders Yuli Osipovich Martov. This text is the foreword written by Martov for the Russian translation of the «Collectivism» speech delivered by J. Guesde, the French Socialist. The illegal publication of this speech undertaken by Martov’s circle inaugurated transition of the circle members from ideologically undefined Radicalism to Marxism. Then when Martov was 20 years old he enunciated political principles he considered to be of highest priority. Martov remained to be loyal to these principles to the grave: the total rejection of the «conspiracy tactics» in struggle for power and the unconditional, independent value of struggle for democracy.