This article analyses the contribution of European socialism to the building of a variegated network of reformers in municipal politics from the end of the nineteenth century to the 1950s. Unsuccessful as a network inside the Second International, a broader international federation of cities, the Union Internationale des Villes/International Union of Local Authorities (UIV/IULA), was proposed in 1913. Belgian, French, Dutch and English socialist leaders remained strongly influential in this federation between the two world wars, working in connection with co-operative movements and the International Labour Office based in Geneva. The fifty years of debates and projects animated by the international journal Les Annales de la Régie Directe founded by the French socialist Edgard Milhaud allows us to follow the development of a generation of local reformers from the beginnings of municipalist thought and praxis up to the idea of building a decentralised European Community of cities and regional authorities.