Since most beers contain barley, which is a grain, they do contain gluten. Some beers, however, are gluten-free and safe for consumption by those with a gluten or wheat allergy.
Part of the confusion that arises from the question of whether or not beer is gluten-free is attributable to the fact that the capability currently only exists to test for one type of gluten protein. This means that foods and drink that contain other types of gluten protein go undetected. Beer falls under this classification. It is recommended that people with wheat or gluten allergies consume only those beers that have been certified as gluten-free.