This work reviews the plant proteins which stimulate the sweet receptor in humans and primates. Identification of the sweet site of thaumatin is a promising target. Thaumatin as a sweetener and flavor enhancer has been used in a wide range of foods. Some of recombinant sweet proteins have been expressed in microbes below economically viable levels. Significance of high-quality production of sweet proteins in higher plant is discussed. Thaumatin and thaumatin-related family have been characterized.