Whilst sociology contains theories of action it is hard to find anything resembling a theory of agency, the difference being that while the former refers to what an actor is doing the latter refers to the actor’s ability to do anything at all. A survey of the different sociological theories that purport to study action reveals that the majority have little to say about action as a real physical event, focusing instead on communication or such cerebral activities as negotiating meanings or taking decisions. Such theories thus fail to reflect the real subjective meaning that action has for the actor, neglecting the important part played by emotion, imagination, or effort. Alexander’s critique of theories of action is then discussed in the context of the need to distinguish adequately, not simply between action and agency but also action and behaviour, with voluntarism understood as the capacity for willed voluntary action. In summary, the lack of a theory of agency is shown to be the reason for the inability of theories of ‘action’ to reflect its true nature as a physical event. This book is thus an attempt to remedy this situation by attempting to develop such a theory.