There has been a resurgence of interest in pulmonary rehabilitation mainly because the prevalence of COPD has increased, scientific studies document consistent benefits (increased exercise endurance and reduced dyspnea), and thoracic surgeons recognize that preoperative and postoperative conditioning enhances the results of lung volume reduction surgery and lung transplantation. Although education and psychosocial/behavioral interventions are important components of a multidimensional program, exercise training of the upper and lower extremities is essential to achieve the described improvements. Current programs vary considerably in the frequency, intensity, and duration of exercise reconditioning. Two "key" questions relating to pulmonary rehabilitation are as follows. What is an appropriate training intensity? How should patients monitor the training intensity? Maintenance exercise programs and the development of home- or community-based programs will be important future developments.