Nurses' discourse about knowing the patient emerged as a recurring theme in an interpretive phenomenological study of the development of expertise in critical care nursing. The purpose of this article is to present analyses related to the meaning of knowing the patient, and its role in everyday nursing practice. Informants in the study were 130 nurses who practiced in adult, pediatric and newborn intensive care units of eight hospitals in three metropolitan areas. The data were group interviews in which nurses gave narrative accounts of exemplars from their practice; in addition, a sub-sample of 48 nurses were observed in their practice and participated in intensive personal history interviews. Knowing the patient means both knowing the patient's typical pattern of responses and knowing the patient as a person. Knowing the patient is central to skilled clinical judgment, requires involvement, and sets up the possibility for patient advocacy and for learning about patient populations.