The field of psychological assessment has been undergoing rapid change. The second edition of this Handbook, published in 1990, appeared at the beginning of a decade marked by extensive advances in assessment in essentially all of its specialized areas. There are many new tests, new applications of established tests, and new test systems. Major revisions have appeared of established tests, notably the Wechsler intelligence scales. The time seemed right for a third edition, since even over the relatively brief period of ten years, many tests described in the second edition have been replaced, and are no longer commonly used. Furthermore, much new research in such areas as neuropsychology, cognitive science, and psychopathology have made major impacts on how many tests and other assessment procedures are used and interpreted. This third edition represents an effort to give the reader an overview of the many new developments in assessment, while still maintaining material on basic psychometric concepts in order for it to continue to serve as a comprehensive handbook for the student and professional.