Gluten is a protein that naturally occurs in some grains. This protein acts as a binding agent when wheat flour is used for baking. The most well-known source of gluten is wheat. When you make wheat into flour, gluten is created. A majority of baked products are made with wheat because the gluten provides a very nice texture once the flour is cooked. Wheat flour is the basis for many products that are commonplace in the western diet. Other grains contain gluten as well. For example, barley, rye and triticale have gluten. Some oats have gluten, but not all.