Registries of patients with pulmonary arterial hypertension (PAH) have been instrumental in characterizing the presentation and natural history of the disease and provide a basis for prognostication. Since the initial accumulation of data conducted in the 1980s, subsequent registry databases have yielded information about the demographic factors, treatment, and survival of patients and have permitted comparisons between populations in different eras and environments. Inclusion of patients with all subtypes of PAH has also allowed comparisons of these subpopulations. We describe herein the basic methodology by which PAH registries have been conducted, review key insights provided by registries, summarize issues related to interpretation and comparison of the results, and discuss the utility of data to predict survival outcomes. Potential sources of bias, particularly related to the inclusion of incident and/or prevalent patients and missing data, are addressed. A fundamental observation of current registries is that survival in the modern treatment era has improved compared with that observed previously and that outcomes among PAH subpopulations vary substantially. Continuing systematic clinical surveillance of PAH will be important as treatment evolves and as understanding of mechanisms advance. Considerations for future directions of registry studies include enrollment of a broader population of patients with pulmonary hypertension of all clinical types and severity and continued globalization and collaboration of registry databases. (J Am Coil Cardiol 2013;62:D51-9) ©2013 by the American College of Cardiology Foundation.