The study of migration has become the cornerstone of the geographical to international movement, with certain major exceptions. Quite why this should be so is puzzling, but it can be suggested that it reflects the relatively scant attention to international migration paid by social scientists generally until the last couple of decades. It is only since about 1970. with large flows in Europe being particularly influential, that the subject has been widely regarded as a problem has ensured the dominance of political-economic approaches to causation.