Pulmonary arterial hypertension (PAH) is a condition that predominantly affects the pulmonary arterial bed, leading to pulmonary vascular remodeling, progressive decrease in pulmonary arterial compliance, and increase in pulmonary vascular resistance. The symptoms of PAH are nonspecific, which often contributes to diagnostic challenges and significant delays in establishing the diagnosis. The investigation of PAH is extensive and involves thorough search for potential clinical conditions that may contribute to its development, as well as the exclusion of other causes of pulmonary hypertension. The proper hemodynamic definition of PAH requires right heart catheterization (RHC) and direct measurements of mean pulmonary artery pressure, pulmonary arterial wedge pressure, cardiac output, and pulmonary vascular resistance. Additionally, RHC allows the assessment of the severity of the disease and, in selected cases, the identification of patients with a positive pulmonary vascular vasoreactivity test. RHC also provides valuable longitudinal information for risk stratification and patient follow-up. In the current manuscript, we review the PAH diagnostic workup, including a detailed review of the most up-to-date recommendations for right RHC and patient risk stratification.