The timing of a book is a curious thing. Sometimes the book appears as a herald to a field, the first inkling that a new theory or new approach has arrived. It points the way, outlines the territory, and energizes workers who may be interested but not quite know how to proceed. Or a book may serve as a capstone to a discipline, the last word (and work) of an overmature area.

More often, however, books appear in a middle position, somewhere between the beginning and the ending of research in an area. Books of this sort attempt to make explicit or to redirect theoretical and empirical efforts, explaining what the authors do for the benefit of other workers in the field. These workers, in turn, usually have some sense of the growing enterprise, but desire to know more, to understand the limits and tensions, the ways in which the particular theory or new approach fits in or contrasts with more widely accepted approaches.

Although we are not certain that all will agree, we envision this volume as a book of the middle variety – an explication, reexamination, and elaboration of an area that has existed for some time. Granted, a hardy band of developmentally oriented workers has for 20 plus years pursued issues such as similar sequences and structures in retarded individuals, the two-group approach, and motivational–personality functioning in retarded individuals.