Psychology is one of the most fascinating fields of study. A field as broad as psychology, which stretches from the study of brain cells to that of prison cells, is an active, argumentative, and exciting adventure that offers opportunities in science, practice, and social policy. Most of the pressing economic and social issues of our generation, such as the environment, health needs, poverty, and violence, will only be alleviated if we understand the ways in which people create or creatively solve the problems that we bring upon ourselves. Psychological testing, assessment and treatment is the discipline of scientific psychology devoted to the study of a given human subject (or group of subjects) in a specific applied field (clinical, educational, work, etc.) by means of scientific tools (tests and other measurement instruments), with the purpose of answering clients¿ demands that require scientific operations such as describing, diagnosing, predicting, explaining or changing the behavior of that subject. We hope this encyclopedia will provide useful information that will help psychologists, psychiatrists, counselor & others understand this fascinating field and its opportunities.