The migration of country dwellers towards the urban areas has been a most important factor in the development of the West European society in which we live today. Therefore, those engaged in research and policy making in the social field must acquire a better under standing of this form of migration if they are to deal effectively with a number of the problems confronting them. This is particularly true since the schemes for European integration which are going ahead so rapidly are sure to produce new patterns of migration. At a meeting of the F.A.O. Working Group on Rural Sociology held in Oslo in 1960, it was suggested that an inventory should be made of all available data and studies on the subject of migration in Europe. This suggestion was taken up by the European Society for Rural Sociology and the Netherlands Ministry of Social Work which, after deliberating together, decided to ask the Dutch expert, Dr. G. Beijer, to draw up such an inventory under their joint auspices. As secretary of the Research Group for European Migration Problems (R.E.M.P.), Dr. Beijer has been engaged for many years in an intensive study of the phenomenon of migration.