This book provides value to anyone interested in theory-for understanding why it exists, why it exists in the form it does, what it is (and what it is not), how to do it and when and where, and the responsibilities it entails. It is useful for those studying theory (or the philosophy of science), for those writing theory, for those critiquing theory, and for those trying to understand and apply theory. The book provides perspective in this ‘thing’ (theory) that is ubiquitous, species-differentiating, and yet deeply flawed in many ways-the thing that undergirds humanity’s greatest successes and continued failures. It demystifies the heart of ‘science’, while unifying the ‘sciences’ in terms of goals and duties.