This thesis investigates the link between the ideological transformations experienced by the Spanish and Portuguese Socialist Parties (PSOE and PS) in the mid-1970s and the relations of these parties with the British Labour Party (BLP) and the French Socialist Party (PSF). The PSOE and the PS underwent similar ideological transformations. They went from advocating Socialism in freedom, rupture with capitalism, international neutralism, self-management and closer relations with the Communists, to practically accepting liberal democracy and the placement of their countries in the West as well as rejecting collaboration with the Communist parties. These transformations happened in the context of the Iberian transitions to democracy in which the main international actors concerned with maintaining Cold War détente got involved. The aim of this thesis is to determine to what extent and how the BLP and the PSF, both representatives of different ideological tendencies within the Western European Socialism, influenced the ideological transformation of the PSOE and the PS. Adopting a transnational and comparative approach and using the theory of cultural transfers, this thesis traces and identifies the circulation of ideas, concepts and practices between the Iberian Socialist parties and their European counterparts. It argues that both the PSOE and the PS were deeply influenced by the French Socialists and their ideas on the rupture with Capitalism, self-management and the union between Socialists and Communists. This was a cause of concern for the main European Social Democrat parties (the BLP and the German SPD), who made a political, diplomatic and economic effort to counterbalance the French influence on the Iberian Socialists, especially regarding the issue of the union of the Left. This turned the Socialist parties of the Iberian Peninsula into a battlefield for two different conceptions of democratic Socialism. As a result, the PSOE and the PS received, adopted, rejected and adapted ideas and practices from these two European tendencies that they applied to their own social, political, cultural and historical realities. If at the beginning of the 1970s both parties were more in tune with the French Socialists than with the European Social Democracy, at the end of the transitions to democracy both of them moved closer to the Western European Social Democrat parties, without completely abandoning some of the ideas, concepts and rhetoric borrowed from the French.