Lung or heart-lung transplantation is a viable option for diverse end-stage pulmonary parenchymal or pulmonary vascular disorders. However, mortality associated with lung transplant (LT) is appreciable, with 3 and 5 year survival rates of approximately 60 and 50%, respectively. Thus LT is reserved for patients with life-threatening disease refractory to medical therapy. Four diagnoses (i.e., chronic obstructive pulmonary disease; idiopathic pulmonary fibrosis; cystic fibrosis; alpha-1-antitrypsin deficiency emphysema) account for approximately 80% of LT recipients; diverse interstitial and pulmonary vascular disorders account for the remaining cases. Given the potential morbidity and mortality associated with LT, the decision to refer patients for LT is difficult. Which patients are acceptable candidates for LT? What are the projected benefits of LT? What criteria should be used to estimate mortality with medical therapy alone? Given the uncertainty of waiting time, when should patients be listed for LT? Identifying appropriate candidates for LT and determining when to list for LT is determined by a risk analysis of the likelihood of mortality during the projected waiting period versus the likely mortality following LT. In this review, we discuss the major diseases treated with LT and the appropriate criteria for LT.