This study is an attempt to fill the lacuna left by the lack of detailed research into the use, by French Trotskyist trade union militants, of the agitational tactic known as the united front. I analyse the manner in which the tactic has been used, evaluate its success or otherwise and assess whether it continues to be of relevance for Trotskyists in the present day. I make use of a range of sources, including archived primary materials and documented memoirs of participants, contemporary media reports, academic research and interviews with Trotskyist activists. An examination of the theory and development of the united front is undertaken, followed by an evaluation of its practical implementation, through consideration of a number of case studies from different periods in the twentieth century. These are, firstly, the short-lived Hotchkiss strike committee, established during the 1936 Popular Front period. Secondly, I evaluate two examples from the immediate post-war period, the Caudron factory workers’ council between 1944 and 1948, and the strike committee established during the Renault factory strike of 1947. Thirdly, I consider the united fronts, in the form of workers’ coordinations, during the period between 1986 and 1995. I draw out and highlight common features between the united fronts, and assess whether or not the tactic made an effective contribution to the winning of industrial disputes by workers and whether, in the process, it enabled Trotskyist activists to generate a receptive audience for their wider political and social ideas. Finally, I consider whether the building of united fronts continues to be a realistic, relevant, practical tactic for Trotskyists in the French trade unions, and one which assists them to effectively pursue their stated longer-term goal of a revolutionary transformation of society.