Helmets sold in the U.S. for street use must meet the criteria of Federal Motor Vehicle Safety Standard (FMVSS) 218, the official DOT standard. Like any other products manufactured to DOT standards such as lights, turn signals and wheels, a helmet model is not actually tested or certified to meet FMVSS 218 before it can be sold; the honor system is used. It's up to the manufacturer to test whatever is necessary to determine if the helmet meets the standard and then label it thus. The DOT, through the National Highway Traffic Safety Administration (NHTSA ), relies on independent, random testing of helmets obtained from retail outlets to police the standard. What this means is that I could make helmets from papier mach here in my office, put DOT labels on the back and sell them on eBay as meeting the DOT standard. Everything would be fine and no one would know otherwise until the helmets were chosen for random testing-if they were even chosen. Snell, on the other hand, tests and certifies sample helmets before they are released to the public, in addition to conducting random sampling. The Snell sticker affixed to the liner means the helmet model has in fact passed the tests and is approved by the Snell Foundation. Judging from the list of helmets that fail the random NHTSA testing and are recalled each year (see www.nhtsa.dot.gov/cars/testing/comply/fmvss218), a DOT sticker on a helmet is certainly no guarantee that it meets the standard.