Taste plays an important role for organisms in determining the properties of ingested substances by conveying important information on five basic taste modalities—sweet, salty, sour, bitter, and umami. Sweet, salty, and umami taste modalities convey the carbohydrate, electrolyte, and glutamate content of food, indicating its desirability and stimulating appetitive responses. Sour and bitter modalities, on the other hand, convey the presence of acidity and potential toxins, respectively, stimulating aversive responses to such tastes. In recent years, the receptors mediating sweet, bitter, and umami tastes have been identified as members of the T1R and T2R G-protein-coupled receptor (GPCR) families, while the molecular mechanisms underlying sour taste have yet to be clearly elucidated. We review aspects of perception and anatomy of acid taste, and explore the various molecules and mechanisms proposed to mediate the detection of sour stimuli.