  The three original publications in this thesis encompass various aspects in
the still developing area of noncommutative quantum field theory, ranging from
fundamental concepts to model building. One of the key features of
noncommutative space-time is the apparent loss of Lorentz invariance that has
been addressed in different ways in the literature. One recently developed
approach is to eliminate the Lorentz violating effects by integrating over the
parameter of noncommutativity. Fundamental properties of such theories are
investigated in this thesis. Another issue addressed is model building, which
is difficult in the noncommutative setting due to severe restrictions on the
possible gauge symmetries imposed by the noncommutativity of the space-time.
Possible ways to relieve these restrictions are investigated and applied and a
noncommutative version of the Minimal Supersymmetric Standard Model is
presented. While putting the results obtained in the three original
publications into their proper context, the introductory part of this thesis
aims to provide an overview of the present situation in the field.
