From the end of the First World War to the late 1930s, the political and social conditions of life in the countries of Maghreb – Morocco, Algeria and Tunisia – were turned upside down under French authority. The colonial issue progressively became a crucial item on the French political scene, as a number of men from the colonized population started to raise precise demands in the name of the peoples of the Maghreb. Although the three Algerian departments and the two protectorates were administered by different authorities and along specific lines, the French Parliament debated Republican policy in the Maghreb as a whole. Within this framework, the Socialist Party’s position presents a number of features. There was no great coherence within the colonial thought of the Socialist group in the National Assembly. Some representatives, such as Marius Moutet, were open to the claims of the colonized people; others, such as Georges Barthélémy, staunchly defended the interests of the settler population. The relative incoherence of the Socialist group’s colonial doctrine was also apparent in its different treatment of the three Maghrebi countries. During the Rif War, for example, Socialist members of Parliament expressed some sympathy towards the Abdelkrim movement, but finally supported the military response to the independentist movement. They also seemed to be open-minded towards the Tunisian claims for self-government. Their attitude to Algeria, with its large settler population and legal status as part of the metropole, was necessarily different. Under the Popular Front, Socialist views on the Algerian problem evolved, but the Socialist deputies went on being reluctant to important change in the « Muslims »’ conditions of living. This paper uses the records of parliamentary debates to account for the Socialist group’s behavior in relation to other parties (particularly during times of crisis), and the archives of the Socialist parliamentary group to retrace the importance of the colonial issue and the range of opinion on the nationalist question in the Maghreb in the party’s internal debates. It addresses the following questions: what were the main features of Socialist colonial doctrine? How did the specific circumstances of the three Maghrebi countries influence Socialist thought? Were comparisons impossible between the Tunisian, Algerian and Moroccan cases? And was the Socialist group entirely unable to think up colonial reforms, and blind towards the colonized peoples’ rights and demands, when it came to regions other than Algeria?