A Mashgiach (Hebrew: משגיח‎, pl. משגיחים, mashgichim, lit. "Supervisor") is a Jew who supervises the kashrut status of a kosher establishment. A mashgiah may supervise any type of food service establishment, including slaughterhouses, food manufacturers, hotels, caterers, nursing homes, restaurants, butchers, groceries, or cooperatives. The mashgiach usually works as the on-site supervisor and inspector, representing the kashrut organization or a local rabbi, who actually makes the policy decisions for what is or is not acceptably kosher. Sometimes the certifying rabbi (Hebrew: רב המכשיר, rav hamachshir) acts as his own mashgiach; such is the case in many small communities.

The usual requirements for becoming a mashgiach are being Jewish, observing the sabbath (shomer Shabbat), observing the laws of kashrut (shomer kashrut), and doing mitzvot, the commandments of the Torah (shomer mitzvot). Different rabbis will have different requirements. Even the same rabbi may have different requirements, depending on the type of establishment being supervised (for example, supervision of a slaughterhouse will be very different from supervision of a grocery). Sometimes the only requirement is that the person is Jewish and knowledgeable of the laws of kashrut. The observant Jew can be a man or a woman.