Naturally gluten-free foods and manufactured gluten-free products that do not contain gluten and meet the FDA standard of under 20 ppm of gluten, can be labelled as “gluten-free”. 
The FDA regulates all except: meat products, poultry products, egg products, and mixed food products that contain more than 3% raw meat or 2% or more cooked meat or poultry. These foods are regulated by the USDA. Allergen and gluten-free labeling of USDA food is voluntary. Allergen labeling of foods regulated by FDA is mandatory.
The FDA rule for gluten-free labeling is voluntary but defines and sets conditions on the use of the term “gluten-free” in foods, including:
- Foods that inherently do not contain gluten (e.g., raw carrots or grapefruit juice) may use the “gluten-free” claim.
- Foods with any whole, gluten-containing grains (e.g., spelt wheat) as ingredients may not use the claim;
- Foods with ingredients that are gluten-containing grains that are refined but still contain gluten (e.g., wheat flour) may not use the claim;
- Foods with ingredients that are gluten-containing grains that have been refined in such a way to remove the gluten may use the claim, so long as the food contains less than 20 ppm gluten/has less than 20 mg gluten per kg (e.g. wheat starch);
- Foods may not use the claim if they contain 20 ppm or more gluten as a result of cross-contact with gluten containing grains.
Health Canada (HC) and Canadian Food Inspection Agency (CFIA) are responsible for the regulation of all foods including mealt, poultry, and egg products. Canada’s Food and Drug Regulations (FDR) requires a complete list of ingrdients on the label and if an ingredient or a component of the ingredient contains any protein, modified protein, or protein fraction that is derived from gluten sources (barely, rye, triticale, wheat, kamut or spelt) – it must be declared on the food label.
The ingredient must be declare in common language, such as semolina (wheat)in in the ingredient list or in a “contains“ statement.
The FDR regulations for labeling a product gluten-free have been in effect since 1995. They have recently been revised to allow for the inclusion of oats as gluten-free if they meet the regulation standard of under 20 ppm gluten.
There are many grains and foods that naturally do not contain gluten and can be safely consumed by individuals with celiac disease. The naturally gluten-free grains include rice, corn, buckwheat, millet, amaranth, oats, quinoa, tapioca, sorghum and teff. Additionally plain potatoes, legumes, many dairy products, meat, fish, poultry, eggs, oils, fruit and vegetables are naturally gluten-free. A healthy balance diet can be created using these naturally gluten-free foods.
There is also a wide range of commercially prepared gluten-free products including mixes, bread, pasta, cookies, crackers, cereals, etc. These manufactured products can be identified by the "gluten-free" designation on the packaging.
The notation of gluten-free by US or Canadian regulations ensures that the product does not contain more than 20 ppm gluten gluten threshold .
Gluten-free products from Europe
Products with a gluten content of less than 20 mg/kg (20 ppm) may use the designation "gluten-free". In addition, manufacturers may also use the symbol of an ear of wheat with a cross through it, which is awarded by coeliac disease groups. However, this is a voluntary designation and is not a guarantee that the product is gluten-free. The only valid symbol is that awarded by the Association of European Coeliac Societies (AOECS). Since the end of 2013, the German Coeliac Society (DZG) has exclusively offered manufacturers European license contracts, with which products can be exported to other countries. If a manufacturer has signed a European contract with the DZG or another European coeliac disease group there is a three-digit registration number under the ear of wheat symbol. Foods that are naturally gluten-free are not marked.
Use EU regulation No. 609/2013 here
May contain traces of ...
There are some foods that are risky even though neither gluten nor products containing gluten are mentioned in the list of ingredients. The risk of contamination with gluten during the production process warrants a warning of the potential risk. 
An example of such risk would be a chocolate factory that also produces chocolate cookies. A may contain statement alerts the consumers of the risk of cross contact with the gluten containing ingrdients. However, under FDA regluations the may contain statement is voluntary and manufacturers are not required to disclose cross contact between the food product and the potential risk of gluten contact.
- FDA/CFSAN, “Gluten-Free Labeling of Foods, Final Regulatory Impact Analysis and Regulatory Flexibility Analysis,” 2013
- Health Canada – Gluten Free labeling regulation. http://www.hc-sc.gc.ca/fn-an/label-etiquet/allergen/index-eng.php
- Thompson, T., Lee, AR, Grace, T. Gluten Contamination of Grains, Seeds, and Flours in the United States; A Pilot Study. JADA 2010; 110:937-940