Capnography provides continuous, dynamic assessment of the ventilatory status of patients. Carbon dioxide physiology and the technology utilized in end-tidal carbon dioxide monitor devices are reviewed. Clinical applications with regard to ventilation and airway management are discussed, including: verification of endotracheal tube placement, continuous monitoring of tube position, monitoring during procedural sedation and in the obtunded patient, and assessment of patients with respiratory illnesses. Current guidelines for use of capnography within emergency medicine are included. Potential future applications are also presented.