The term „mixity“, most often qualified by either „functional“ or „social“, has taken on a prominent position in the field of public policies on housing. It has come to represent the antidote to social or ethnic segregation as well as the trend in urban zoning that has separated housing, work places, and shops and services. “Zoning” in urban planning is criticized for favoring social segregation and generating an explosion of individual mobility. These critiques have amplified in the past few years with the rise in ecological concerns and the demands of sustainable development. A large scale consensus is forming in support of the development of “functionally mixed” urban spaces. This new space associates brings together the different functions („work“, „housing“, „consumerism“, „leisure“) into close proximity, which in turn reduces the need for motorized mobility and favors the development of low-impact, collective modes of transportation. This functional mixity also favors social mixity. Though the causality between functional mixity and social mixity can be called into question, on a more fundamental level, it is the very notion of social mixity that interests the scientific community. Numerous academics however have reservations concerning its definition. First, how can a situation of mixity be best assessed and researched? Then, there is the question of what can be qualified as mixed housing. Do we focus on mixing generations, ethnic communities, or the « rich and the poor »? Furthermore, its innovative nature is called into question for, under other terms, hasn't “diversity” and “social intermingling” been a predominant concern of public policies in another era? Finally, there is the question of end results. What is the aim of social mixity? Does it want to fight the imprisonment of “self-segregation”, to encourage new ties, or to favor social cohesion? Though researchers are very hesitant on a form of ideal mixity, one that is supposed to remedy the ills of contemporary society (segregation, ghettoisation, the dislocation of social ties, matching with its peers), they are even more dubitative on the normative or prescriptive dimension of social mixity’s injunction, one that inspires a certain number of public policy’s dispositions. Nevertheless, in the name of mixity, myriad efforts are currently undertaken in urban contexts: for example, within urban renovation or regeneration policies, or in the framework of the redistribution of social housing. Though we can question the very pertinence of the notion of mixity and its ideological foundations, it is also interesting to consider what its implementation produces. Beyond its mobilizing effect, does it render the manner in which housing is organized more efficient and effective? What does it produce, « side by side » situations or social interactions? Mobilizing academic debate from various European countries is all the more interesting in that Europe contains highly differentiated conceptions of what it means to live together and the status or the recognition to be given to diversity, especially ethnic diversity.