This chapter focuses on recent developments in the understanding of the structure and functionality relationships of soy proteins. Seed proteins play an important role in food consumption worldwide. Soy proteins have been utilized for many kinds of traditional foods. The use of soy protein products as functional ingredients is gaining increasing acceptance in food manufacturing from the standpoints of human nutrition and health. The seed proteins of legumes, including soybeans, are albumins and globulins. Globulins, the dominant storage proteins, account for about 50–90% of seed proteins. Storage globulins are grouped into two types according to their sedimentation coefficients: 7S globulins and 11S globulin. The ratio of 11S to 7S globulins varies among cultivars. It is about 0.5–1.7 in soybean. The 11S globulins, legumin-type proteins, are widely distributed in many legume and nonlegume seeds and are generally simple proteins, although there are some exceptions; for example, lupin 11S globulin is a glycosylated protein.