Capnography or end-tidal carbon dioxide (Etco₂) monitoring has a variety of uses in the pediatric intensive care setting. The ability to continuously measure exhaled carbon dioxide can provide vital information about airway, breathing, and circulation in critically ill pediatric patients. Capnography has diagnosis-specific applications for pediatric patients with congenital heart disease, reactive airway disease, neurologic emergencies, and metabolic derangement. This modality allows for noninvasive monitoring and has become the standard of care. This article reviews the basic principles and clinical applications of Etco₂ monitoring in the pediatric intensive care unit.