The 6th World Symposium on Pulmonary Hypertension (WSPH) Task Force has updated the haemodynamic definitions and clinical classification of pulmonary hypertension (PH). Previously, PH was defined as mean pulmonary arterial pressure (mPAP) ≥25 mmHg at rest, measured by right heart catheterisation. Recent data show that normal mPAP in healthy individuals is 14.0 ± 3.3 mmHg, with two standard deviations above this value suggesting mPAP >20 mmHg as above the upper limit of normal. This definition is now based on scientific evidence rather than being arbitrary. However, mPAP alone is not sufficient to define pulmonary vascular disease, as it can be due to increased cardiac output or pulmonary arterial wedge pressure. The Task Force proposes including pulmonary vascular resistance (PVR) ≥3 Wood Units in the definition of all forms of pre-capillary PH associated with mPAP >20 mmHg. In clinical classification, the Task Force introduced a subgroup of pulmonary arterial hypertension (PAH) long-term responders to calcium channel blockers and a subgroup of PAH with overt features of venous/capillary involvement. These changes reflect the need for a more accurate and simplified classification system. The updated classification includes group 1 (PAH), group 2 (PH due to left heart disease), group 3 (PH due to lung diseases and/or hypoxia), group 4 (PH due to pulmonary artery obstructions), and group 5 (PH with unclear and/or multifactorial mechanisms). Group 5 was simplified by removing splenectomy and thyroid disorders, and LAM-associated PH was classified with other parenchymal lung diseases in group 3. The Task Force also discussed the role of exercise in PH, noting that while exercise PH was previously included in the definition, it is now considered less relevant due to uncertainties about its clinical significance. The updated classification emphasizes the importance of right heart catheterisation for accurate diagnosis, including measurements of cardiac output and pulmonary arterial wedge pressure. The Task Force concluded that the new definitions and classification system provide a more accurate and clinically relevant framework for the management of PH.The 6th World Symposium on Pulmonary Hypertension (WSPH) Task Force has updated the haemodynamic definitions and clinical classification of pulmonary hypertension (PH). Previously, PH was defined as mean pulmonary arterial pressure (mPAP) ≥25 mmHg at rest, measured by right heart catheterisation. Recent data show that normal mPAP in healthy individuals is 14.0 ± 3.3 mmHg, with two standard deviations above this value suggesting mPAP >20 mmHg as above the upper limit of normal. This definition is now based on scientific evidence rather than being arbitrary. However, mPAP alone is not sufficient to define pulmonary vascular disease, as it can be due to increased cardiac output or pulmonary arterial wedge pressure. The Task Force proposes including pulmonary vascular resistance (PVR) ≥3 Wood Units in the definition of all forms of pre-capillary PH associated with mPAP >20 mmHg. In clinical classification, the Task Force introduced a subgroup of pulmonary arterial hypertension (PAH) long-term responders to calcium channel blockers and a subgroup of PAH with overt features of venous/capillary involvement. These changes reflect the need for a more accurate and simplified classification system. The updated classification includes group 1 (PAH), group 2 (PH due to left heart disease), group 3 (PH due to lung diseases and/or hypoxia), group 4 (PH due to pulmonary artery obstructions), and group 5 (PH with unclear and/or multifactorial mechanisms). Group 5 was simplified by removing splenectomy and thyroid disorders, and LAM-associated PH was classified with other parenchymal lung diseases in group 3. The Task Force also discussed the role of exercise in PH, noting that while exercise PH was previously included in the definition, it is now considered less relevant due to uncertainties about its clinical significance. The updated classification emphasizes the importance of right heart catheterisation for accurate diagnosis, including measurements of cardiac output and pulmonary arterial wedge pressure. The Task Force concluded that the new definitions and classification system provide a more accurate and clinically relevant framework for the management of PH.