  We give a self-contained introduction into the metric-affine gauge theory of
gravity. Starting from the equivalence of reference frames, the prototype of a
gauge theory is presented and illustrated by the example of Yang-Mills theory.
Along the same lines we perform a gauging of the affine group and establish the
geometry of metric-affine gravity. The results are put into the dynamical
framework of a classical field theory. We derive subcases of metric-affine
gravity by restricting the affine group to some of its subgroups. The important
subcase of general relativity as a gauge theory of translations is explained in
detail.
