The purpose of this study was to further explicate the Dreyfus Model of Skill Acquisition in the practice of critical care nursing. For this analysis data were used from a sample of 105 nurses practicing in the adult, pediatric, and newborn intensive care units of eight hospitals in three metropolitan areas. The data were composed of group interviews in which nurses gave narrative accounts of exemplars from their practice and close observations and intensive personal history interviews of a subsample of nurses. Two interrelated aspects were found to distinguish four levels of practice, from advanced beginner through expert. First, practitioners at different levels of skill literally live in different clinical worlds, noticing and responding to different directives for action. Second, a sense of agency is determined by one's clinical world and shows up as an expression of responsibility for what happens with the patient.