Historical and sociological accounts of migration have often influenced each other. The article investigates the sociological tradition of research on the subject, showing how it came to be constructed as a specialism concerned almost exclusively with the immigration of foreigners. The sociology of immigration has a peculiar position within sociology, adopting methods associated more with the Chicago School or with antrhopology than is usually the case in sociological studies of the majority population. This difference in the methods and background assumptions used for studying "communities" of immigrants from abroad (or from the countryside in the past) has led to some misunderstandings. For in reality many of the patterns identified in the study of immigrants - chain migration, occupational specializations, geographical concentration, etc. - are present in modified form also in thoroughly "modern" populations. The article illustrates this briefly with reference to migrant French young people who cannot be suspected of major cultural difference from the majority population, and do not suffer discrimination. Research on migration thus constitutes an important source of concepts for understanding social and historical processes more generally, not just for understanding foreigners or peasants.