  Starting from the Ginsparg-Wilson relation, a general construction of chiral
gauge theories on the lattice is described. Local and global anomalies are
easily discussed in this framework and a closed expression for the effective
action can be obtained. Particular attention is paid to the non-abelian gauge
anomaly, which is shown to be related to a local topological field on the
lattice representing the Chern character in 4+2 dimensions.
