Pulmonary function tests (PFTs) determine how well the lungs work. They measure how much air goes into and out of the lungs, how much air goes from the lungs to the blood, and how well the lungs work during exercise.Office spirometry is the most commonly practised PFT, measuring lung function, specifically the volume and/or speed air can be inhaled and exhaled.Fractional Exhaled Nitic Oxide (FeNO) devices are a novel medical technology used in the diagnosis of asthma. FeNO devices measure fractional exhaled nitric oxide in the breath of patients. Nitric oxide is a biomarker for asthma which provides an indication of the level of inflammation in the lungs.Impulse oscillometry is a test that uses sound waves to measure how much resistance there is to the normal movement of air in and out of the lungs when breathing at rest.A lung diffusion test (DCLO) uses a gas containing carbon monoxide to measure how much oxygen moves from the lungs to the blood when inhaling. The test is used to help diagnose lung conditions and measure how well treatments are working.Technical parameters and quality control are of paramount importance in appropriate use of PFTs.This book provides clinicians and trainees with an overview of PFTs, guiding them through the science and clinical application of different methodologies, to help with diagnosis and management of a variety of respiratory conditions.