As we have stated repeatedly, the purpose of this book is to review the research on the psychological effects of aerobic fitness training. For this purpose, we use a quantitative reviewing technique termed meta-analysis. This approach to literature reviews is relatively new, and the reader might be somewhat unfamiliar with the logic and method of meta-analysis. Therefore, before dealing with the review itself, it was deemed appropriate to acquaint the reader with the historical background, development, and methods unique to meta-analysis, with special emphasis on the differences between this approach and that of more traditional research reviews.