Nattō is a traditional Japanese food made from whole soybeans that have been fermented with Bacillus subtilis var. natto. It is often served as a breakfast food with rice. It is served with karashi mustard, soy or tare sauce, and sometimes Japanese bunching onion. Within Japan, nattō is most popular in the eastern regions, including Kantō, Tōhoku, and Hokkaido.

The soybean, soy bean, or soya bean is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses.