Pulmonary hypertension (PH) has historically been defined as a mean pulmonary artery pressure (mPAP) ≥ 25 mm Hg measured by right heart catheterization (RHC).The Sixth World Symposium on Pulmonary Hypertension (6th WSPH) in 2018 proposed a new hemodynamic threshold of mPAP > 20 mm Hg. A number of reasons led to the proposed change in the hemodynamic definition of PH. The change in hemodynamic definition of PH poses new challenges in the field. The updated definition will lead to increased case finding of patients with PH. It has the potential to identify patients with PH at an earlier stage of the disease, and optimistically, permit introduction of therapeutics at an earlier timeframe with potential to improve outcomes. PH is divided into 5 major groups for clinical classification purposes. These are: 1) Pulmonary Arterial Hypertension (PAH); 2) PH due to left heart disease; (3) PH due to lung disease and/or hypoxia (PH-LD); 4) PH due to pulmonary artery obstruction and 5) PH with unclear and/or multifactorial mechanisms. In addition to hemodynamic differences, the groups encompass a broad range of underlying conditions, with varied prevalence and therapeutic approach.