  The purpose of this of this paper is to develop the theory of Eisenstein
series in the framework of geometric Langlands correspondence.
  Our construction is based on the study of certain relative compactification
of the moduli stack of parabolic bundles on a curve suggested by V.Drinfeld.
  As an application we construct certain automorphic forms for global fields of
positive characteristic, whose existence is non-obvious from the point of view
of classical tools.
