Unified Theories of Cognition by Newell presents the theoretical ground-work of SOAR, one of the most important cognitive architectures ever developed (the others being ACT-R by Anderson, EPIC by Kieras, and CAPS, now 4CAPS, by Thibadeau, Just, Carpenter, and Varma). This book and papers/texts of ACT-R, EPIC, and 4CAPS, and the SOAR Project form the foundation of those interested in the field of cognitive architectures and provides the strongest possible foundation for those interested in graduate school and research in this area of a.i. Those interested in the most recent revisions to the theory and applications should consult the SOAR website.