Wee felt it before in sense; but now wee know it by science. Edward Misselden (1623) The collective effort reported in this volume is the outcome of the diffusion of the idea of diffusion as a fundamental process in society. The considerable number of disciplines represented here indicates the weight of the problem area. The editors are to be congratulated for their initiative in drawing together present thinking at a vivid meeting, now also in print. An old timer in the business has not much to add. But maybe some things, bearing in mind that a Preface is a celebration and not a review. As...