Chronic Obstructive Pulmonary Disease is the leading cause of morbidity and mortality. In 2000, WHO estimated that COPD was the fourth leading cause of death worldwide. As per prediction of WHO, by year 2020 COPD will be the third leading cause of death and the 5th leading cause of disability. Pulmonary function tests are used to diagnose COPD. As WHO says, by 2020 COPD will be the 5th leading cause of disabilty, it makes study of functional capacity of the diseased an important aspect. This book speaks, how COPD affects pulmonary functions and functional capacity of the patient. And how routine treatment plays its part with evidence.