The whole purpose of the respiratory system, which includes the nose, pharynx, trachea, bronchi and lungs, is to allow the intake of fresh air into the lungs, where oxygen is absorbed and carbon dioxide discharged. Respiratory function is basically a clinical area where the scientist with some knowledge of many aspects of physics and engineering can help the clinician in the diagnosis of disease. This chapter covers the basic principles of the techniques found in most respiratory function laboratories with the exception of the techniques of blood gas analysis. It explains the basic physiology of respiration and some of the methods of measuring respiration, including the principles of the instrumentation involved. The chapter provides a discussion on respiratory monitoring found outside the respiratory function laboratory in areas such as the intensive care unit, special baby care units and in research situations.