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The issue of migration has spawned abundant research and prompted wide-ranging theoretical debate. A selection of papers, articles and book chapters spanning several decades, many of which were first written in English, have been translated into French and brought together in a book published by INED as part of a new series devoted to the founding texts of demographic theory. These texts were chosen for their original contributions to the discipline. They represent landmarks of demographic thought, and provide new insights for analysing and understanding demographic processes. The inaugural volume of this series was edited by Victor Piché. In an introductory chapter, of which this article is an abridged and slightly revised version, he places these founding texts in their historical perspective. He highlights the diversity of approaches applied to understanding migration: countries of origin or destination; micro, meso and macro levels; individual behaviours, networks, migration policies. He also shows how these theories have evolved to take account of changing local and international migration dynamics. This article explores the development of contemporary migration theories as reflected in some twenty founding texts that have marked the field over the last fifty years. (1) Before proceeding further, two points must be made clear. First, by founding texts, we refer to the landmark articles or book chapters that have shaped the progress of migration studies. They are constantly recurring references, both in the theoretical frameworks used by scholars in their empirical studies, and in the numerous literature reviews offering critical overviews of these theories. The second point concerns the period covered, namely the decades from the 1960s up to the year 2000. Of course, by choosing this period,(1) The 20 texts brought together in the collective work published by INED are identified in the text and the bibliography by an asterisk (*). Piché V., Les Théories de la migration, Paris, INED, les Manuels / Textes fondamentaux, 536 p., available at www.ined.fr/en

After thirty years of research into Rendu-Osler-Weber disease, the authors review the contributions of the three successive approaches used to analyse this rare genetic disorder. First, historical demography sees patients as markers of past migration and population transfers. Starting out from a cluster of cases straddling the Ain and Jura départements, the history of this population group was reconstituted on the basis of civil records, and their migration to other parts of France was studied by looking for family ties between the initial group and the cases observed elsewhere in the country. Second, epidemiology and population genetics give estimates of prevalence by département that are higher than those initially predicted in 1977, the start year of this study. They also provide statistical tools to test hypotheses of a single or multiple origin for the disease by looking for a common ancestor among affected families. Last, molecular biology provides a means to identify the genes responsible for the disease and their various mutations, thus confirming the existence of several different origins.