  We review the theory of hard exclusive scattering in Quantum Chromodynamics.
  After recalling the classical counting rules which describe the leading scale
dependence of form factors and elastic reactions at fixed angle, the
  pedagogical example of the pion form factor is developped in some detail in
order to show explicitely what factorization means in the QCD framework. The
inclusion of transverse degrees of freedom leads to the discussion of Sudakov
effects which are crucial for protecting the calculation from dangerous
infrared regions. The picture generalizes to many hard reactions; a strategy to
extract distribution amplitudes from future data is sketched. We discuss also
the particular case of hadron-hadron collisions where the independent
scattering mechanism dominates asymptotically and where a different
factorization formula applies. We briefly present the concepts of color
transparency and nuclear filtering and critically discuss the few present data
on this subject.
