As each of the 15 sections of this Survey opens with an editorial introduction, the prologue is more limited in intention. I want principally to provide some justification for the selection of topics, regions and periods. In this respect, it is only proper to start with a modicum of modesty. Despite this being a very ambitious project, no one editor and no one volume can hope to encompass all the manifold aspects and all the major examples of human migration. It is simply too vast a subject. The description ‘survey’, rather than ‘encyclopaedia’, has been used to indicate that neither the publishers nor the editor claim complete comprehensiveness. At the same time, we have covered a good deal of ground. The Survey contains 95 contributions by 99 authors from 27 countries. The authors' home disciplines range across most of the humanities and social sciences. We can thus legitimately claim that this book provides the most representative and wide-ranging coverage of migration ever attempted in a single volume.

However, comprehensiveness alone was regarded as insufficient. We rejected the short anodyne entries typical of a one-volume encyclopaedia in favour of ‘midi-sized’ contributions (of 2000 to 5000 words) which allowed authors to develop an argument without being too prolix. This inevitably involved fewer, but more targeted, topics. How then were editorial decisions made? After wrestling with a number of alternatives, the overriding conclusion reached was that no single criterion for selection would work. In practice, to reflect the complexity of the phenomenon of migration itself, a number of organizing principles had necessarily to go hand in hand. I will discuss, in turn, issues of period, place, forms of migration and differing approaches.