The hospital critical care unit provides an authentic, high-stakes setting for studying reasoning, argumentation, and discourse. In particular, it allows examination of structural and pragmatic features of informal collaborative argument created while participants are engaged in familiar, meaningful activities central to their work. The nursing change of shift report is a workplace ritual which includes communication of extensively detailed patient data and nursing decisions as well as the justifications for those decisions. Nurse pairs (N = 20 pairs) from three hospitals and four critical care units were observed and recorded during authentic change of shift reports, then interviewed or surveyed about the reporting process. The nurses in this study showed a number of argumentative strengths including frequent use of evidence to back claims and the construction of a complex and nuanced process for achieving agreement about the patient situation. Nursing variations from traditional structural argument models, including emphasis on first-hand information and efforts to reach agreement, are effective pragmatic strategies for justifying claims related to patient care in a dynamic, time-pressured environment. The study of nursing workplace discourse has implications for progress in argumentation and educational psychology as well as nursing education and health care delivery.