One of the main theorems concerning gerbes is their cohomological classification whenever they have automorphism groups given by a fixed sheaf of abelian groups formula_45, called a band. For a gerbe formula_2 on a site formula_22, an object formula_48, and an object formula_49, the automorphism group of a gerbe is defined as the automorphism group formula_50. Notice this is well defined whenever the automorphism group is always the same. Given a covering formula_51, there is an associated classformula_52representing the isomorphism class of the gerbe formula_2 banded by formula_54.