Statistical Measure, Policy Measure - The Case of Rough Sleepers: Since the 1980s, in the US and Europe, various statistical methods have been developed to investigate people without housing, including those who sleep in places “not meant for habitation”, the “rough sleepers”. Street counts can be done locally by local authorities or by organizations serving homeless people to assess policies toward the rough sleepers or seeking to attract the attention of the general public and authorities. Among national statistical agencies, national street counts of rough sleepers are carried out and highlighted by a civic type of argument. A third type of surveys involves a vision of the rough sleepers as occupying a situation which may be only transitory, and involves public action to improve the situation of homeless people, but also to prevent it. By drawing on the work of Alain Desrosières, we will attempt to reconsider these statistical tools, these ways of thinking about society, and these policies of acting on society, at least for the fraction of interest here.