The authors propose a classification of knowledge that they call case, patient, and person and that reflects the content of the knowledge necessary to the conduct of nursing work. This classification represents an attempt to theorize from their respective empirical research data. Case knowledge is general knowledge of pathophysiology, disease processes, pharmacology, and other therapeutic protocols. Patient knowledge is that knowledge that defines the individual within the health care system, the knowledge expressed in the individual's response to therapeutics, and the knowledge that enables nurses to move the recipient of care through the health care system and along the illness trajectory. Person knowledge is knowledge of the individual as a subject with a personal biography who occupies a certain social space and who acts with his or her own desires and intentions for reasons that make sense to him or her. Two types of social knowledge serve as relational knowledge, or a bridge that links case knowledge to patient knowledge and patient knowledge to person knowledge. Each type of knowledge is accessed differently and the extent to which each is attained and used is determined by the circumstances of the patient's illness and his or her location in the health care system. The authors make a case for why this classification might be useful to the discipline.