Pulmonary hypertension is defined as an increase of the mean pulmonary arterial pressure above 25 mm Hg and, as such, the diagnosis requires invasive haemodynamic measurement by right heart catheterisation. More than just a single disease, pulmonary hypertension is an umbrella term that includes many different disorders and pathophysiological entities. However, most forms of pulmonary hypertension share a final common pathway, in particular the trias of vasoconstriction, microthrombosis and vascular remodelling. The classification of pulmonary hypertension has been subjected to many changes within the last decade. At the same time, major achievements in our understanding of the complex pathobiology have been made. Here, these developments are discussed in the light of the recently published report from the fifth World Symposium on pulmonary hypertension.