This article analyses the Communist party of Chile's (PCCh) political shift from "class against class", practised from 1928 to early 1935, to the Popular Front, adopted in 1935 and consolidated in 1936. During the years that the PCCh was outlawed under the dictatorship of General Carlos Ibanez del Campo (1927-1931) the PCCh split into two rival groups. The dispute resulted in the permanent division of Chilean communists in 1933: the faction backed by the BSA adopted the sectarian orientation of "class against class" and maintained the name of the party; the dissidents founded the Communist Left thereby strengthening their links with the international Trotskyist movement. The policy of "class against class" had developed little during the Ibanez dictatorship and the isolationist line that was adopted was disinclined to establish alliances with other anti-dictatorial forces. However, from mid 1931, due to the increasing influence of the BSA in the direction of the official communist faction, this isolationist line manifested itself in an even more belligerent sectarianism regarding other left wing movements and indirectly encouraged insurrectional actions of different types being generated without direct regard to the official orientation of the party. Nevertheless, from 1932 a change began to take place which can be seen in joint actions with other sectors and was an endogenous precedent for the move towards the popular front policy, officially adopted by the Seventh Comintern Congress of 1935. The PCCh's new strategy of alliances was the result of a variety of factors both internal (the need to end its isolation and transform itself into a party of the masses) and external (the new directives of the Communist International, in line with international policies of the Soviet Union). Thus, when the Comintern moved more decidedly towards a policy change, there already existed a certain favourable predisposition in the PCCh and there arose no organised resistance from within the PCCh to the changes promoted by Moscow. The Chilean emissaries of the Communist International and the Profintern only had to overcome their reluctance on specific aspects of the new orientation, such as the extension of the field of alliances, which related rather to the persistence of sectarian conceptions, habits and behaviours, remnants of the orientation "of class against class" in the consciences of the Chilean communists, and did not constitute an articulated opposition to the popular front.