Introduction or preface

The notion of "causal web" emerged in the epidemiological literature in the early Sixties and had to wait until the Nineties for a thorough critical appraisal. Famously, Nancy Krieger argued that such a notion isn't helpful unless we specify what kind of spiders create the web. This means, according to Krieger, (i) that the role of the spiders is to provide an explanation of the yarns of the web and (ii) that the sought spiders have to be biological and social. This paper contributes to the development of the notion of causal web, elaborating on the two following points: (i) to catch the spiders we need multi-fold evidence - specifically, mechanistic and difference-making - and (ii) for the eco-social approach to be explanatory, the web has to be mechanistic in a sense to be specified.