The School of Proximity has provided a comprehensive picture and a systematic analysis of the dimensions, characteristics, and fields of application of the principle of proximity. Its analytical assessment is the main object of this introduction to the Handbook of proximity relations. We start to show that interest in proximity-related questions is the result of a long process through which scientists became aware of the value of this notion, and which has led to its gradual autonomization in the field of social sciences. Then are presented the main features of the School of Proximity, the story of the field of research, its theoretical variations, its ramifications, its conceptual stabilization and its inclusion in social sciences analysis. We give a canonical definition of proximity relationships by distinguishing between the two major polar categories - geographical and organized proximity – and identifying key achievements of this approach. We finally discuss the disciplinary approaches that are inspired nowadays by this approach, before opening the agenda of future research, in terms of analytical refinements and further extensions.