The calcium-sensing receptor, CaSR, is a key regulator of blood calcium homeostasis. Its physiological actions are well understood but its influence on behavior has not been appreciated until recently. Many animals have a specific calcium appetite [1], which implies they can detect calcium and consume sufficient of it to meet their needs. To determine how they do this, we exploited inbred strains of mice that differ in their avidity for calcium [2]. A genome scan and studies with congenic and knockout mice revealed that calcium consumption is under the control of two genes coding for the so-called “sweet taste” receptor, T1R3, and for CaSR [3,4,5]. This and other findings have led us to propose that the CaSR has two roles in behavioral calcium regulation. First, the motivation to seek and ingest calcium is regulated by alterations in blood calcium that are detected by the CaSR in the subfornical region of the brain. This is based on (a) strong expression of the CaSR in the subfornical organ, (b) involvement of the subfornical organ in related behaviors such as the appetite for sodium, (c) electrophysiological studies showing that the subfornical organ is sensitive to calcium and CaSR agonists, and (d) ablation studies showing that destruction of the subfornical organ attenuates calcium appetite. Second, the CaSR influences the consumption of calcium by acting as a taste receptor on the tongue. Evidence for this is based on (a) observations by three groups that CaSR is present in taste receptor cells of rats and mice, (b) the differential expression of CaSR in taste tissue of calcium-preferring and calcium-avoiding strains of mice, and (c) the differential response of these mice to CaSR agonists. T1R3 dimerizes with T1R2 to produce a receptor sensitive to sweeteners, and it dimerizes with T1R1 to produce a receptor sensitive to umami (glutamate) taste. Perhaps a T1R3-CaSR heterodimer detects oral calcium. Whatever the mechanism, the existence of an oral calcium detector raises intriguing issues, including the question of whether calcium should be considered a basic taste.