I know wheat is the common problem when avoiding gluten, but what about other grains, like barley, rye, or oats? 
Note that wheat is a type of grass, and is technically a grain.  Grains without gluten  Not all grains have gluten—only those closely related to wheat do.  Grains which do not have gluten include:   Corn (maize) and its variants or derivatives such as cornmeal, polenta, hominy, or masa Rice (all varieties)  A note on rice: some varieties are called "glutinous". This just sounds similar to "gluten", but is in fact used to indicate the rice's stickiness. Glutinous rice does not have gluten, not even as traces, its stickiness comes from a special type of starch.  Millet Sorghum Oats (although many oat products are processed in plants that may have had wheat)   Sometimes confused for grains  Note that the following gluten free seeds are not grains, although sometimes they are confused for grains:   Wild rice Quinoa Buckwheat (despite the name, not a wheat nor a grain) Amaranth   Non-grains used as gluten-free starches and flours  Therefore, all grain-like, starchy, or flour-type foods which are not grasses are always gluten free, including wild rice, quinoa (despite any other issues), and so on.  Additionally, flours or seeds based on non-grain seeds, nuts, and legumes are always gluten free, although there may be other dietary sensitivities.  These include:   Almonds Soy beans Peanuts Chickpeas  Mesquite flour Amaranth Quinoa Wild rice   Finally, starches and flours based on roots, rhizomes, and so on are gluten free, including:   Potato Sweet potato (True) yams Tapioca   Grains containing gluten  The following grains are all wheat relatives, and have gluten to a greater or lesser degree:   Wheat Spelt Rye Tritical Barley Kamut   Note that the following are all processed wheat products or specific wheat varieties, and should be avoided to maintain gluten free diets:   Farina Durum Semolina Couscous      See also:     Gluten Free Living WebMD guide to gluten free flours  