A comprehensive review is provided of substances of plant origin that are known to be highly sweet-tasting, with isoprenoids, flavonoids, and proteins being the major compound classes represented. Several of these substances have commercial use in one or more countries. Of these, the diterpene glycoside rebaudioside A was assigned generally recognized as safe status in the United States in 2008. A review of naturally occurring compounds that either enhance or inhibit the sweet taste sensation is presented. Techniques for the discovery of natural sweeteners and modifiers of the sweet taste are described, in addition to methods for their sensory evaluation using volunteer human subjects. Finally, the interaction of natural products with the recently characterized sweet receptor is discussed.