A gluten-free diet is recommended amongst other things in the treatment of celiac disease and wheat allergy. It is a diet completely free of ingredients derived from gluten-containing cereals: wheat (including kamut and spelt), barley, rye, and triticale, as well as the use of gluten as a food additive in the form of a flavoring, stabilizing or thickening agent. Additionally, the diet may exclude oats. Some people for whom the diet is recommended can tolerate oat products and some medical practitioners say they may be permitted, but there is controversy about including them in a gluten-free diet because studies on the subject are incomplete.

Several grains and starch sources are considered acceptable for a gluten-free diet. The most frequently used are maize, potatoes, rice, and tapioca (derived from cassava). Other grains and starch sources generally considered suitable for gluten-free diets include amaranth, arrowroot, millet, montina, lupine, quinoa, sorghum (jowar), sweet potato, taro, teff, chia seed, and yam. Various types of bean, soybean, and nut flours are sometimes used in gluten-free products to add protein and dietary fiber. In spite of its name, buckwheat is not related to wheat; pure buckwheat is considered acceptable for a gluten-free diet, although many commercial buckwheat products are actually mixtures of wheat and buckwheat flours, and thus not acceptable. Gram flour, derived from chickpeas, is also gluten-free.

Gluten is also used in foods in some unexpected ways, for example as a stabilizing agent or thickener in products like ice-cream and ketchup.

People wishing to follow a completely gluten free diet must also take into consideration the ingredients of any over-the-counter or prescription medications and vitamins. Also, cosmetics such as lipstick, lip balms, and lip gloss may contain gluten and need to be investigated before use.