In the last ten years the problem of homelessness has been on the increase. Compared to the situation about sixty years ago the homeless of today congregate more in the centres of the big cities, adhere to a different lifestyle and are socially, culturally and ethnically more diverse. Some indications of the scale of the problem in the Netherlands are given, but the focus of the paper is on the role of psychiatry: on the one hand, in providing services to the mentally ill among the homeless and, on the other hand, in protecting communities against people who are considered bothersome or unfit for civil life. The development of systems of comprehensive care for different categories of socially marginal people is discussed.