  In this paper, we will describe the mathematical foundation of topological
Landau-Ginzburg (LG) models coupled to gravity at genus 0 in terms of primitive
forms. We also discuss the mirror symmetry for Calabi-Yau manifolds and CP^1 in
our context. We will show that the mirror partner of CP^1 is the theory of
primitive form associated to f=z+qz^{-1}.
