Made from fermented soybeans, soy sauce (shoyu in Japanese and jiàng yóu in Chinese) is the basic condiment of all the cuisines of East Asia. It was first made in China 2,500 years ago, probably discovered by chance, using a liquid produced by the fermentation of soybeans, water, and salt. It turned out to have a pleasant flavor of meat, the eating of which was forbidden by Buddhist teachings. In the 7th century, soy sauce was introduced to Japan, where it quickly became very popular, but it was later made milder with the addition of wheat. Japanese soy sauce was introduced into Europe by the Dutch in the 17th century. Vatel served it during a banquet for King Louis XIV of France. In the following centuries, the Chinese and Japanese expanded its use throughout the world. Soy sauce has become more diverse, flavored with spices, and is now as commonplace a condiment as mustard and ketchup.

Soy sauce can be bought from supermarkets and Asian grocery stores. There is a vast range: light-colored, traditional, strong, sweet. These varieties depend on the country of origin and production process. A good-quality soy sauce should be amber brown and slightly translucent; it should have a good consistency (neither too thick nor too liquid, but syrupy); it should have a slightly toasted smell with notes of citrus and vanilla, and its flavor should be fresh, light, and well balanced. Of the Japanese sauces, koikuchi is the most common, and is quite dark in color. Usukuchi is less strong, light in color, and does not stain food. Tamari soy sauce is a little thicker and darker. Chinese soy sauces come in two varieties: one is dark (colored with caramel), very aromatic, with a delicate taste; the other is quite light, quickly made, and often contains additives. Industrial soy sauces are mostly of poor quality, made too quickly without fermentation, and often artificially colored. Although soybeans are mostly grown from GM varieties, it is possible to buy GMO-free soy sauces.

Soy sauce is ideal for use in hot preparations and can be added at the start of cooking.

Soy sauce is used to enhance all types of dishes: salads and soups through vegetables, fish, meat, rice, pasta, and other grains. Mixed with wasabi, soy sauce is a traditional seasoning for sushi and sashimi.

A bottle of soy sauce should be stored at room temperature.

While soy sauce has little particular nutritional interest, it contains a lot of histamine (developed during fermentation) and therefore may trigger an allergic reaction in some people. Furthermore, all types are very high in salt, because they are made using brine.

Japanese soy sauce is produced in a series of stages. The soybeans are first washed and steamed. They are then crushed and mixed with roasted (and crushed) wheat and yeast. The resulting puree is called koji, and is left to ferment for a few days. Once fermented for the necessary amount of time, brine is added to produce moromi. This is left to marinate for anywhere between six months and two years (depending on the desired strength of the sauce). The sauce is then filtered, pasteurized, and bottled. Chinese soy sauce is made in a different process. The washed soybeans are directly marinated in brine for differing amounts of time, from a few months to several years. Darker sauces are the result of longer marinating times. Some sauces are flavored with spices or oyster. Hoisin sauce, or barbecue sauce, which is often thick and a reddish color, is made by adding chile and spices to soy sauce.