This inquiry is concerned with the themes of praxis and action in four philosophic movements: Marxism, existentialism, pragmatism, and analytic philosophy. It is rare that these four movements are considered in a single inquiry, for there are profound differences of emphasis, focus, terminology, and approach represented by these styles of thought. Many philosophers believe that similarities among these movements are superficial and that a close examination of them will reveal only hopelessly unbridgeable cleavages. While respecting the genuine fundamental differences of these movements, this inquiry is undertaken in the spirit of showing that there are important common themes and motifs in what first appears to be a chaotic babble of voices. I intend to show that the concern with man as an agent has been a primary focal point of each of these movements and further that each contributes something permanent and important to our understanding of the nature and context of human activity.