Cover (IMAGE) SAGE Caption What concepts shape the contemporary study and practice of psychology? Analyzing key theorists and theories in the field, The SAGE Encyclopedia of Theory in Psychology contains information on the theories' histories, strengths, and weaknesses. The SAGE Encyclopedia of Theory in Psychology is out today as a two-volume set. Credit SAGE Publishing Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.