A summary of the ontological foundations of Activity Theory introduces a critical review of the work of activity theorists across the world with a focus of applications in medical and educational contexts, and concludes with a review of the ethics of collaboration. Blunden expands the domain of Activity Theory to address the pressing problems facing humanity today and activities lacking in clear objects, collaboration in voluntary projects and social movements, the life projects of individuals and emerging practices. Blunden brings an understanding of Marxist and Hegelian philosophy to bear on the application of Activity Theory to problems of social change.