Non-perturbative effects are responsible for the
essential dynamical features of the four-dimensional gauge theories such as
QCD.  The N=2 supersymmetric four-dimensional theories are an interesting
class of models in which non-perturbative computations can be carried out with
arbitrary precision using localization of the path integrals. I will explain
the new exact non-perturbative results and the relation to classical and
quantum integrable systems for a large class of N=2 supersymmetric QCD.