Some years ago a book reviewer, perhaps with Freudian honesty, remarked that the book in question 'filled a much needed gap in the literature'. That phrase has haunted the writing of this gap-filler and this preface may be considered an apologia. For a number of years I have found myself teaching various groups of students about cell locomotion and cell behaviour: sometimes science students specializing in cell or molecular biology, sometimes immunologists or pathologists who only wanted a broad background introduction. Those students who were enthusiastic, or who wished to appear so, asked for a general background text (to explain my lectures perhaps), and that is what I hope this book will provide. With luck, other scientists who have only a peripheral interest in cell movement will also find this a useful overview. The more proximate origin of the book was a special 'option' subject which I taught for two years to our Senior Honours Cell Biology students in Glasgow.