Na⁺/HCO₃⁻ cotransporter NBCe1 is an electrogenic member of the solute carrier 4 (SLC4) family and plays important roles in intracellular pH regulation as well as transepithelial HCO₃⁻ movement. The physiological and pathological significance of NBCe1 has been well established by genetic studies with humans as well as knock-out study with mouse. NBCe1 is expressed in diverse tissues in mammals. The transporter plays an essential role in the maintenance of acid-base homeostasis in our body, being responsible for more ~80% of HCO₃⁻ reabsorption in the proximal renal tubule. In humans, a number of SLC4A4 mutations have been associated with proximal renal tubule acidosis that is often accompanied with short stature, ocular abnormalities (including cataract, glaucoma, and band keratopathy), migraine, and/or defects in dental enamel development. In the present article, we review the molecular physiology, the structure/function relationship, the mechanisms underlying the functional regulation of NBCe1, as well as the physiological and pathological roles of the transporter.