Endothelial cells line all blood vessels and regulate the contractility of smooth muscle cells to tune regional organ blood flow and systemic pressure. Chloride (Cl^–) is the most abundant anion in endothelial cells, yet the molecular identities and physiological functions of Cl^‑ channels in endothelial cells are poorly understood. I will describe our recent work where we generated tamoxifen-inducible, endothelial cell-specific TMEM16A channel knockout mice to investigate signaling mechanisms and physiological functions of this Cl^‑ channel in this cell type. Our data indicate that TMEM16A channels generate Ca²⁺-activated Cl^‑ currents in endothelial cells. Vasodilators stimulate TMEM16A channels in endothelial cells, leading to arterial hyperpolarization, vasodilation, and a reduction in blood pressure. I will also provide evidence that TMEM16A channel activation reduces intracellular Cl^– concentration, which stimulates With-No-Lysine (WNK), a Cl^‑-sensitive kinase, in endothelial cells. WNK kinase signaling then activates transient receptor potential V4 channels in endothelial cells to induce vasodilation.