Why buy a book on engineering design first published nearly thirty years ago? Because it remains up-to-date, intellectually stimulating and realistic. Unlike most texts in the field, it relates design closely to the science and mathematics that are students' chief concern, and shows their relevance. It shows how to make simple but illuminating calculations such as mark the work of great engineers, and how to achieve insight and the invention that often springs from it. It covers design principles thoroughly: these are a great practical aid to designers but receive only limited mention elsewhere. It is, and remains, an original book. Though some of the ideas in it which were novel in 1971 are now widely accepted, others remain new.