Pulmonary arterial hypertension (PAH) is a syndrome in which pulmonary arterial obstruction increases pulmonary vascular resistance, which leads to right ventricular (RV) failure and a 15% annual mortality rate. The present review highlights recent advances in the basic science of PAH. New concepts clarify the nature of PAH and provide molecular blueprints that explain how PAH is initiated and maintained. Five basic science concepts provide a framework to understand and treat PAH: (1) Endothelial dysfunction creates an imbalance that favors vasoconstriction, thrombosis, and mitogenesis. Restoration of this balance by inhibition of endothelin and thromboxane or augmentation of nitric oxide (NO) and prostacyclin is the paradigm on which most current therapy is based. (2) PAH has a genetic component. Mutations (bone morphogenetic protein receptor-2 [BMPR2]) and single-nucleotide polymorphisms (SNPs; ion channels and transporter genes) predispose to PAH. (3) Excess proliferation, impaired apoptosis, and glycolytic metabolism in pulmonary artery smooth muscle, fibroblasts, and endothelial cells suggest analogies to cancer. Many experimental therapies reduce PAH by decreasing the proliferation/apoptosis ratio; these include inhibitors of pyruvate dehydrogenase kinase (PDK), serotonin transporters (SERT), survivin, 3-hydroxy-3-methylglutaryl coenzyme A reductase, transcription factors (hypoxia-inducible factor [HIF]-1 and nuclear factor of activated T lymphocytes [NFAT]), and tyrosine kinases. Augmentation of voltage-gated K channels (Kv1.5) and BMPR2 signaling also addresses this imbalance. Tyrosine kinase inhibitors used to treat cancer are currently in phase 1 PAH trials. (4) Refractory vasoconstriction may occur due to rho kinase activation. Fewer than 20% of PAH patients respond to conventional vasodilators; however, refractory vasoconstriction may respond to rho kinase inhibitors. (5) The RV can be targeted therapeutically. Although increased afterload initiates RV failure, which is the major cause of death/dysfunction in PAH, the RV may be amenable to cardiac-targeted therapies. The RV in PAH has features of ischemic, hibernating myocardium. Guided by these new concepts and armed with a better understanding of disease mechanisms, we are poised to identify new therapeutic targets. To achieve balance in a rapidly evolving field, we invited colleagues to contribute Figures and legends illustrating pathways in their area of expertise that are important to the pathogenesis and treatment of PAH. These contributors are acknowledged in the Acknowledgments section.