This book is by a professional for other professionals, but thoughtful people who are interested in the fundamental aspects of human nature will also find much to interest them. The papers which have been published in various journals or delivered to professional audiences since the appearance of Frances Tustin's previous book Autistic Barriers in Neurotic Patients are integrated with unpublished material written especially for this book, so that they can enrich and illuminate each other. A paper from the early days of her work with autistic children is the focus of this present work, since her awareness of encapsulation as being the major protective reaction associated with the autistic states of both psychotic and neurotic patients, has stemmed from that early paper.