Pulmonary hypertension often complicates the course of patients with advanced lung disease, and it is associated with a worse prognosis. In the recent classification of pulmonary hypertensive disorders, pulmonary hypertension due to lung disease is considered as a separate category within a group of disorders that were previously referred to as “secondary”. The incidence and clinical course of pulmonary hypertension associated with chronic obstructive pulmonary disease is best known among the pulmonary hypertension associated with lung diseases. The pathophysiology and treatment of pulmonary hypertension seen in the course of advanced lung diseases are generally distinct from those of pulmonary arterial hypertension. Chronic hypoxia is the major mechanism implicated for the development of pulmonary hypertension in patients with lung diseases. This article focuses on the recent advances in our knowledge about the pulmonary hypertension due to lung diseases or hypoxia.