Chronic thromboembolic pulmonary hypertension is a progressive and life-threatening condition that is believed to be related to inadequate dissolution of acute pulmonary thromboemboli, followed by fibrotic organization. Without appropriate treatment, progressive pulmonary hypertension, right ventricular failure, and death may occur. While the disorder was initially described nearly a century ago in autopsy studies, antemortem diagnosis became feasible with the advent of cardiac catheterization and angiography techniques in the 1940s, while surgical thromboendarterectomy was not attempted until the 1960s. However, this procedure initially had high mortality rates until refinements in management and surgical techniques resulted in much improved outcomes starting in the 1980s. Many questions remain about the pathophysiology and epidemiology of this condition, with unclear contributions of genetics and environmental exposures. The optimal approach to diagnosis also continues to evolve, with improvements in preoperative imaging and hemodynamic assessment. Treatment of chronic thromboembolic pulmonary hypertension has not remained static, as surgical techniques continue to improve and newer pharmacological treatments and percutaneous catheter-based interventions may play therapeutic roles in selected patients. This is the introductory article of a series that provides a state-of-the-art review of chronic thromboembolic pulmonary hypertension.