The book aims to contribute to current debates regarding the idea of labour law. In particular, it aims to assess the validity of the suggestion that old ways of thinking about the subject have become outdated. Detailed consideration is given to two such ‘old ways’: the idea of the labour constitution, developed by Hugo Sinzheimer in the early years of the Weimar Republic, and the principle of collective laissez-faire, elaborated by Otto Kahn-Freund in the 1950s. The question is then addressed as to whether and how these ideas could be abstracted from the political, economic, and social contexts within which they were developed so that they might still usefully be applied to the study of labour law. The central argument of the book is that the labour constitution can be developed so as to provide an ‘enduring idea of labour law’. That argument is constructed against a critique of the work of a number of British scholars who have argued in recent years that labour law scholarship ought to be reorientated to align more closely with the functioning of labour markets. As compared with the posited ‘law of the labour market’, the primary claim made for the idea of the labour constitution is that it highlights the inherently political nature of labour laws and institutions, as well as their economic functions. It provides a framework for analysing labour laws, labour markets, and labour market institutions which does not limit the capacity of scholarship in the field to retain its critical edge.