  This thesis is dedicated to explore the feasibility of numerical calculations
in the $\epsilon$--regime of QCD for the extraction of physical information. We
apply two formulations of the Ginsparg-Wilson fermions the Neuberger operator
and the hypercube overlap operator to compute the observables of interest. As a
main result we present the comparison of the distributions of the leading
individual eigenvalues of the Neuberger operator in QCD and the analytical
predictions of chiral random matrix theory. We observe a good agreement as long
as each side of the physical volume exceeds about $L\approx 1.12\fm$. It turns
out that this bound for $L$ is generic and sets the size of the physical volume
where the axial correlator behaves according to chiral perturbation theory.
This allows us to compute a value for the pion decay constant $F_{\pi}$. As an
alternative procedure we only consider the contribution from the zero modes.
Here we are able to obtain an estimate for $F_{\pi}$ and $\alpha$. As a
theoretical development the L\"uscher topology conserving gauge action is
investigated. This enables us to sample the observables of interest in the
$\epsilon$--regime without recomputing the index. We can report that a
promising gauge action has been identified.

High Energy Physics - Lattice