  This is a version of the author's diploma thesis written at the University of
Cologne in 2002/03. The topic is the construction of Seiberg-Witten invariants
of closed 3-manifolds. In analogy to the four dimensional case, the structure
of the moduli space is investigated. The Seiberg-Witten invariants are defined
and their behaviour under deformation of the Riemannian metric is analyzed.
  Since it is essentially an exposition of results which were already known
during the time of writing, the thesis has not been published. In particular,
the author does not claim any originality concerning the results. Moreover, new
developments of the theory are not included. However, the detailed
account--together with the appendices on the required functional analytic and
geometric background--might be of interest for people starting to work in the
area of gauge field theory.
