Monosodium glutamate (MSG) is an odorless, white crystalline powder used to flavor food. It is the sodium salt of glutamic acid (C 5 H 8 NO 4 Na) and elicits a taste called umami. MSG has been commercially available since 1909 and is used in products like bouillon, instant ramen, canned soup, salad dressings, frozen meals, snack chips and crackers, and low-fat yogurt. In the late 1960s, MSG was blamed for an adverse reaction called “Chinese restaurant syndrome” (CRS). Placebo-controlled studies have found no evidence for CRS, but concerns about the safety of MSG persist, particularly in Western countries. This entry focuses on the commercial production of MSG and its health effects.