This Festschrift marks the retirement of Professor Chris Calladine, FRS after 42 years on the teaching staff of the Department of Engineering, University of Cambridge. It contains a series of papers contributed by his former students, colleagues, and friends. Chris Calladine's research has ranged very widely across the field of struc­ tural mechanics, with a particular focus on the plastic deformation of solids and structures, and the behaviour of thin-shell structures. His insightful books on Engineering Plasticity and Theory of Shell Structures have been appreciated by many generations of students at Cambridge and elsewhere. His scientific contri­ bution outside engineering, in molecular structures, is at least as significant, and he is unique among engineers in having co-authored a book on DNA. Also, he has been keenly interested in the research of many students and colleagues, and on many occasions his quick grasp and physical insight have helped a student, and sometimes a colleague, find the nub of the problem without unnecessary effort. Many of the papers contained in this volume gratefully acknowledge this generous contribution. We thank Professor G. M. l. Gladwell for reading through all of the contri­ butions, Mrs R. Baxter and Mrs o. Constantinides for help in preparing this volume, Godfrey Argent Studio for permission to reproduce Calladine's por­ trait for the Royal Society, and Dr A. Schouwenburg -from Kluwer- for his assistance. Horace R. Drew Sergio Pellegrino ix CHRIS CALLADINE SOME THOUGHTS ON RESEARCH c. R.