Andy Blunden presents a critical review of theories of Concepts in cognitive psychology, analytical philosophy, linguistics, conceptual change theory and other disciplines. The problems in these disciplines has led many to abandon the idea of Concepts altogether, particularly those taking an interactionist approach. Blunden responds with an historical review focussing on the idealist philosophy of Hegel, its reception and transformation in the development of positive science and finally the cultural psychology of Lev Vygotsky. He then proposes an approach to Concepts which draws on Activity Theory. Concepts are equally subjective and objective, units of consciousness and of the cultural formation of which one is a part. This continues the author's earlier work in An Interdisciplinary Theory of Activity (Brill 2010).