Chronic thromboembolic pulmonary hypertension (CTEPH) results from mechanical obstruction of (major) pulmonary vessels by non-resolving thromboemboli. If left untreated, the condition is fatal due to increased right ventricular afterload and right heart failure. Recent advances in the understanding of misguided thrombus resolution, small-vessel pulmonary arteriopathy and the identification of CTEPH risk factors have introduced novel disease concepts. In this chapter, we assemble the relevant literature into a picture of the old and new views of CTEPH evolution. Moreover, the role of established as well as experimental diagnostic tools is reviewed, with an emphasis on imaging techniques that allow visualisation of perfusion defects and differentiation between thromboembolic and non-thromboembolic pulmonary vascular disease. Finally, therapeutic options are discussed. Pulmonary endarterectomy (PEA) is the treatment of choice in patients with confirmed CTEPH. After successful PEA, patients are considered cured, since a vast majority nearly normalise their haemodynamic parameters and exercise capacity. Data on medical treatment of the condition and evidence-based knowledge are put into perspective with current clinical practice.