Further elucidation is required on the validity of action research. The tendency of nurse action researchers to rely on perspectives of validity from qualitative or ethnographic research only gives a partial picture. Three categories of validity regarding action research are proposed in order to develop understandings and to stimulate debate: dialectical, critical and reflexive. Tensions and processes, moral responsibilities, reflexivity and accounts of action research are discussed to illuminate the validity of action research. The complexity and contradictions inherent even when attempting to demonstrate its validity are highlighted and illustrated with reference to examples of action research.