The monograph is the first comprehensive study of the People's Socialist Party (NSP, Enes) in Russian and foreign historiography in 1907-1917. For the first time, the number, composition, organizational state of the Enes party and its local organizations, publishing, sources of funding for the NSP were comprehensively covered and analyzed; the social doctrine and nature of the party's tactics were reviewed in a new way; revealed the adjustments made to them as a result of understanding by the enes of new phenomena of social development of Russia; for the first time, an analysis of the activities of the Enes during the First World War was given; revealed the causes of the so-called "organizational crisis" of the NSP, in relation to the phenomena characteristic of all Russian parties.