This article traces the interactive process between theory and research as it has been used to clarify the concept of self-care agency, a key concept in Orem's model of nursing. Theoretical constructions of self-care agency that have emerged in the work of Orem and the Nursing Development Conference Group are reviewed. Operational measures of self-care agency are described, particularly with regard to their underlying theoretical formulations. Factorial structures for some self-care agency instruments are related to the components of self-care agency in Orem's most recent conceptualization. Dimensions of self-care agency that are consistently supported by research studies of this phenomenon are identified.