Elaborate apparatus plays an important part in the science of to-day, but I sometimes wonder if we are not inclined to forget that the most important instrument in research must always be the mind of man. It is true that much time and effort is devoted to training and equipping the scientist's mind, but little attention is paid to the technicalities of making the best use of it. There is no satisfactory book which systematises the knowledge available on the practice and mental skills—the art—of scientific investigation. This lack has prompted me to write a book to serve as an introduction to research. My small contribution to the literature of a complex and difficult topic is meant in the first place for the student about to engage in research, but I hope that it may also interest a wider audience. Since my own experience of research has been acquired in the study of infectious diseases, I have written primarily for the student of that field. But nearly all the book is equally applicable to any other branch of experimental biology and much of it to any branch of science. – (Cambridge, 1957. W.I.B. Beveridge)