  Holomorphic principal G-bundles over a complex manifold M can be studied
using non-abelian cohomology groups H^1(M,G). On the other hand, if M=\Sigma is
a closed Riemann surface, there is a correspondence between holomorphic
principal G-bundles over \Sigma and coadjoint orbits in the dual of a central
extension of the Lie algebra C^\infty(\Sigma, \g). We review these results and
provide the details of an integrability condition for almost complex structures
on smoothly trivial bundles. This article is a shortened version of the
author's Diplom thesis.
