The importance of this chapter lies in the fact that impairment of respiratory function by obesity is potentially reversible and therefore should be a focus for therapeutic intervention (1-12). This review will be composed of three parts. The ﬁrst will be the description of changes in respiratory mechanics, gas exchange, and control with obesity such as physiological decrements that result in dyspnea, the increased work of breathing, and abnormalities in gas exchange that many obese individuals exhibit. The second part will include a discussion of pathophysiologic staging of respiratory impairment in obesity, using as a basis a classiﬁcation system proposed by Bates (13). The third part will outline the emerging literature on sleep disordered breathing and obesity, obesity and asthma, and the syndrome of obesity hypoventilation.