This chapter explores the philosophical underpinnings of cultural-historical theory. More precisely, this chapter traces the philosophical roots of Vygotsky's theory by focusing mainly on the philosophical ideas of Spinoza, Hegel, Feuerbach, and Marx. Vygotsky found the roots of the crisis in psychology in the failure of Cartesian dualism that was the dominant tendency in the domain of psychology. He was looking for a philosophical theory which allows a radically new look at the key theoretical, methodological, and practical issues raised in psychology as a discipline.