In this analysis of the problem of freedom from a humanistic-Marxist perspective, the author draws on the full chronological spectrum of Marx's writings to reconstruct Marx' mature view of freedom under three broad categories; freedom as a mode of being, freedom as transcendence, and freedom as spontaneity. While recognising that many students of Marx have noted two distinctly different perspectives, Brien interprets Marx's philosophy as a coherent organic whole. He demonstrates that Marx's thought is principally and systematically an elaborated philosophical-scientific theory of freedom. An addendum shows how humanistic Marxism and Buddhism converge on the same basic values and mutually complement each other. This comparison serves to emphasize the viability of projecting a non-theistic spiritual dimension and shows that there is a genuine moral basis for common social action among adherents of different perspectives. This rigorously argued and deeply thoughtful analysis reveals the continuing relevance and promise of Marx's thought in the 21st century.