Aspects are identified which are to be considered when attempting to identify those activities we wish to call nursing. Using conceptual analysis by means of borderline and model cases, an exposition of the nature of nursing is reached. The process of theory building, the function of theories and their application to what has been identified as the sphere of nursing are explained. The relationship of ‘micro theory’ and ‘paradigmatic theory’ are described. The application of theory to nursing education are linked by the use of Peters'(1966) criteria for education. A model attempts to demonstrate the relationships pointed out in the text.