Defining what is understood as habitat participatif (participative or co-housing) in France comes up against regulatory ambiguities and a diversity of regional contexts and micro-local situations. Taking as its starting point a survey carried out in the city of Grenoble, which has a long tradition of cooperation and participatory politics, the article analyzes this diversity to identify the common characteristics of co-housing projects and to attempt to define an ‘ideal type’. The cases are described in relation to the social changes of the twentieth century in order to illustrate the long history of the projects, which are based on a range of ideological principles, but are always characterized by three core concepts: sharing, environmental awareness, and citizen participation.