Background Oral care plays a clear and important role in the prevention of ventilator-associated pneumonia. However, few studies have explored the actual work of oral care by nurses in the intensive care unit. Objective To explore intensive care nurses’ knowledge of and experiences with the delivery of oral care to reveal less visible aspects of this work. Methods In an institutional ethnography, go-along and semistructured interview methods were used to explore the oral care practices and perspectives of 12 bedside nurses and 12 interprofessional (intensivist, allied health, and management) participants in an intensive care unit at a large urban teaching hospital in Ontario, Canada. Results Nurses described how obstacles frequently inhibited the delivery of oral care. Technical barriers included oral crowding with tubes and aversive responses by patients, such as biting. Contextual impediments to oral care included time constraints, lack of training, and limited opportunities for interprofessional collaboration. A key discovery was the presence of an informal unit-based nursing curriculum, whereby nurses acquired strategies to overcome barriers to oral care. Although the nurses did extensive problem solving in providing oral care, the interprofessional participants had limited knowledge of how oral care was accomplished. Conclusion These data suggest the complexity of performing oral care in intensive care is underestimated and perhaps undervalued. Future research is needed to address technical and contextual barriers to optimize current guideline expectations for the provision of regular and effective oral care.