The article offers a fresh approach to assessing the significance of the Communist Party congresses in Yugoslavia by highlighting their legitimising role rather than their presumed political importance. Focusing on the five congresses of the League of Communists of Yugoslavia between 1958 and 1978, the article draws its conceptual framework of the legitimation of power from social theory. Based on the analysis of the congress papers of the leading Yugoslav communists, it questions the role of three sources of legitimacy in justifying communist power: ideology, popular sovereignty, and performance. The article argues that the central source of Yugoslav authorities’ legitimacy was socialist self-management, which was effectively intertwined with the other two sources of legitimacy. Marxist elements were particularly prominent in the late 1950s and in the 1970s, while the importance of the collective will of the people was emphasised fairly uniformly at all the congresses considered. In the 1960s, the element of the regime’s economic efficiency – with the standard of living as the most important component – acquired an important role, which steadily increased until the end of the period under consideration.