  The predictions of the Mirror Symmetry are extended in dimensions n>3 and are
proven for projective complete intersections Calabi-Yau varieties. Precisely,
we prove that the total collection of rational Gromov-Witten invariants of such
variety can be expressed in terms of certain invariants of a new generalization
of variation of Hodge structures attached to the dual variety. To formulate the
general principles of Mirror Symmetry in arbitrary dimension it is necessary to
introduce the ``extended moduli space of complex structures'' M. An analog M\to
H*(X,C)[n] of the classical period map is described and is shown to be a local
isomorphism. The invariants of the generalized variations of Hodge structures
are introduced. It is proven that their generating function satisfies the
system of WDVV-equations exactly as in the case of Gromov-Witten invariants.
The basic technical tool utilized is the Deformation theory.
