The use of capnography has expanded over recent years. Currently, capnography is used in a variety of acute care settings. This article describes what capnography is and how it is used. The normal and abnormal capnogram or waveforms are described to assist in identifying various clinical situations. The multiplicity of clinical indications include detection of pulmonary embolism as well as malpositioned endotracheal/tracheal, gastric, and small bowel tubes. Capnography also provides clinicians with information regarding expiratory breathing patterns and assists in perfusion assessments such as those for cardiopulmonary resuscitation. Finally, case studies are provided to help the reader apply the concepts of capnography to a variety of acute care settings.