There are very few psychologists living today who have contributed more to the advancement of psychology, in general, and to the psychology of language and thought, in particular, than O. Hobart Mowrer. It would indeed be ludicrous to attempt to list the many and varied accomplishments and contributions that Dr. Mowrer has made to his profession over the years. Even the selected essays that are in this volume can only suggest a modicum of his remarkable, vital, and ongo- ing contribution to the psychology of language and thought. Further- more, the chapters in this book, which were published over a period of some twenty-five years, clearly illustrate that Dr. Mowrer was concerned not only with basic research, but that he also had an interest in its application. These chapters also point to the fact that although Dr. Mowrer's orientation was primarily that of a "behaviorist" at the onset, his constant attempts to revise knowledge in this field and broaden its scope make it virtually impossible for us to classify him as a behaviorist in the narrow meaning of that term. The chapter on mental imagery, for example, written only a few years ago, serves to illustrate this point. In addition, the Autism Theory of Speech Development (see Chapter 4), one of Dr.