During his lifetime, W.E. Blatz was so much occupied with the development of the University of Toronto's Institute of Child Study that he was able to devote little time to writing. This is his first book to appear in twenty-one years, and his first complete exposition of his famous Theory of Security. The Theory of Security is radically different from the theories promulgated by Freudian psychologists. Whereas Freudian personality theory is based on the notion of unconscious, an entity that is only indirectly observable, the Theory of Security derives from the observation of the conscious state in all its manifestations. Dr. Blatz thus makes use of both empirical observations and the results of introspection, and, as might be expected, some of his conclusions run counter to those reached in much current psychological discussion. But proof of the forcible influence of the theory and its author may be found in the impressive number of books and articles already published by Dr. Blatz's associates at the Institute of Child Study, applying the theory to the practical problems of psychological observation and therapy. It is fitting that the man whose work has generated so much fruitful research by others in this field should at last have set down in book form the fundamental principles that guided them.