France has experienced massive changes in its regulation of working time during the last decade. These changes generate natural experiments that may help to study a variety of issues in labor economics, including work sharing effect on job creation or productivity, labor relations or adaptation of firms to regulation. This paper provides a primer for researchers interested by working on these issues. It includes detailed information about the 35-hour laws and their progressive removal, and discusses the first wave of research evaluating these policies, that draws a contrasted picture. It also highlights some unexplored lines of research.