This document provides an overview of capnography, which is a technology that objectively measures ventilation by detecting exhaled carbon dioxide. It can be used for both intubated and non-intubated patients to continuously monitor ventilation and the patient's ABCs. The document reviews the history of capnography, from its initial use in operating rooms to new portable technologies suitable for emergency medical services. It also outlines the clinical applications of capnography such as verifying endotracheal tube placement and monitoring treatment effectiveness.