  We revisit the construction of self-dual field theory in 4l+2 dimensions
using Chern-Simons theory in 4l+3 dimensions, building on the work of Witten.
Careful quantization of the Chern-Simons theory reveals all the topological
subtleties associated with the self-dual partition function, including the
generalization of the choice of spin structure needed to define the theory. We
write the partition function for arbitrary torsion background charge, and in
the presence of sources. We show how this approach leads to the formulation of
an action principle for the self-dual field.
