  We present a detailed analysis of the GKZ(Gel'fand, Kapranov and Zelevinski)
hypergeometric systems in the context of mirror symmetry of Calabi-Yau
hypersurfaces in toric varieties. As an application we will derive a concise
formula for the prepotential about large complex structure limits. (Talk given
at the Taniguchi Symposium ``Topological Field Theory, Primitive Forms and
Related Topics'' December, 1996)
