Exhaled air contains numerous substances, often in extremely low concentrations. The development of sensitive detection techniques has made it possible to examine the composition of exhaled air in relation to a variety of airway diseases and other disorders. In this Monograph, an overview of current breath analysis techniques and their clinical applications is provided for the clinician. The various contributions give a fascinating perspective of a future where new, highly sensitive methodologies will enable clinicians to diagnose and monitor a wide variety of diseases merely by taking the patient's breath.