  We use the Regge-Teitelboim method to treat surface integrals in gauge
theories to find global charges in Chern-Simons theory. We derive the affine
and Virasoro generators as global charges associated with symmetries of the
boundary. The role of boundary conditions is clarified. We prove that for
diffeomorphisms that do not preserve the boundary there is a classical
contribution to the central charge in the Virasoro algebra. The example of
anti-de Sitter 2+1 gravity is considered in detail.
