Homotopy G-algebras and moduli space operad

This paper reemphasizes the ubiquitous role of moduli spaces of algebraic curves in associative algebra and algebraic topology. The main results are: (1) the space of an operad with multiplication is a homotopy G- (i.e., homotopy graded Poisson) algebra; (2) the singular cochain complex is naturally an operad; (3) the operad of decorated moduli spaces acts naturally on the de Rham complex $\Omega^\bullet X$ of a K\"{a}hler manifold $X$, thereby yielding the most general type of homotopy G-algebra structure on $\Omega^\bullet X$. One of the reasons to put this operadic nonsense on the physics bulletin board is that we use a typical construction of supersymmetric sigma-model, the construction of Gromov-Witten invariants in Kontsevich's version.