More than 75 years ago, at the Second All-Russian Psychoneurological Congress, L. S. Vygotsky presented a paper, “Methods of Reflexological and Psychological Investigations,” in which he began to lay the foundation for a unified theory of mind. Vygotsky's concern was that psychology had lost sight of the uniqueness of human mental functioning, which for him resides in our ability to intentionally mediate, and hence regulate, our biologically specified mental systems (i.e., in today's jargon, input systems) through culturally determined means. Contemporary sociocultural psychologists, J. V. Wertsch in particular, have noted that, although Vygotsky called for the unification of psychology, in his writings, he actually paid very little attention to one part of the mental equation—the biological, or natural, mind. As it turns out, even those who fault Vygotsky for his failure here have themselves not focused much attention on the contribution of the natural, or what Frawley refers to as the computational, mind, preferring instead to concentrate on the sociocultural parameters of cognition. The present book can be seen as an attempt to bring to fruition Vygotsky's earlier vision of a unified psychology.