We offer an epistemological basis for action research, in order to increase the validity, the practical significance, and the transformational potential of social science. We start by outlining some of the paradigmatic issues which underlie action research, arguing for a “turn to action” which will complement the linguistic turn in the social sciences. Four key dimensions of an action science are discussed: the primacy of the practical, the centrality of participation, the requirement for experiential grounding, and the importance of normative, analogical theory. Three broad strategies for action research are suggested: first-person research/practice addresses the ability of a person to foster an inquiring approach to his or her own life; second-person research/practice engages a face-to-face group in collaborative inquiry; third-person research/practice asks how we can establish inquiring communities which reach beyond the immediate group to engage with whole organizations, communities and countries. The article argues that a transformational science needs to integrate first- second- and third-person voices in ways that increase the validity of the knowledge we use in our moment-to-moment living, that increase the effectiveness of our actions in real-time, and that remain open to unexpected transformation when our taken-for-granted assumptions, strategies, and habits are appropriately challenged. Illustrative references to studies that begin to speak to these questions are offered.