A paradigm shift in our understanding of the pathogenesis of chronic thromboembolic pulmonary hypertension (CTEPH) has recently occurred. We previously believed that recurrent pulmonary embolism might be a major cause of CTEPH. However, recent evidence suggests that venous thromboembolism might be a trigger, and in situ thrombosis in the pulmonary artery and small-vessel vasculopathy (vascular remodeling) similar to pulmonary arterial hypertension (PAH) could be important to the progression of CTEPH. Pulmonary ventilation-perfusion scans are necessary for the screening of CTEPH. Furthermore, contrast CT scans can detect segmental emboli and are useful for the differential diagnosis of pulmonary vascular disease. However, pulmonary angiography is still the gold standard for assessment of surgical accessibility and small-vessel disease. The prognosis of this disease was poor in the 1980s (5-year survival: ~40%). Pulmonary endarterectomy with median sternotomy under intermittent deep hypothermia has decreased operative mortality to <5% at expert centers. Advances in balloon angioplasty techniques have resulted in marked improvement in pulmonary hemodynamics, quality of life, and survival for inoperable patients in Japan. A soluble guanylate cyclase stimulator (riociguat) has just become available for patients with inoperable or persistent/recurrent pulmonary hypertension after surgery. It must be emphasized that this disease is treatable once patients with dyspnea on exercise have been accurately diagnosed with CTEPH.