This chapter describes the pathophysiologic basis and use of capnography in the detection of pulmonary embolism (PE) from a variety of causes. Pulmonary embolism results in an increase in respiratory deadspace, specifically alveolar deadspace, which can be determined with parameters obtained with capnography. Pulmonary embolism results in an occlusion or limitation of flow in the pulmonary vasculature to respiratory units. Pulmonary embolism effects an increase in the physiologic deadspace by increasing alveolar deadspace, a component of the physiologic deadspace. FDlate is determined from fitting the phase III slope portion of the volumetric capnogram. The ability of volumetric capnography to track the resolution of pulmonary emboli with thrombolytic therapy has also been investigated. Evaluation of patients with various parameters derived from capnography holds promise for early bedside non-invasive detection of embolism, thereby allowing prompt and effective therapy.