An overview is given of investigations concerning the epidemiology of Salmonella, carried out at the National Institute of Public Health and Environmental Hygiene in Bilthoven, The Netherlands, during the last thirty years. It is made clear that Salmonella, because of its ubiquitous occurrence and its large variety in sero- and phage-types, is the organism of choice to study the epidemiological pathways of pathogens between man, animals and the environment. It is demonstrated that these are in fact the pathways of faecal contamination, and therefore have validity for a larger number of bacterial, and perhaps even parasitic and viral, micro-organisms. This last statement is illustrated by the presentation of studies on the epidemiology of Campylobacter jejuni.