  Infinite-dimensional Grassmannian manifold contains moduli spaces of Riemann
surfaces of all genera. This well known fact leads to a conjecture that
non-perturbative string theory can be formulated in terms of Grassmannian. We
present new facts supporting this hypothesis. In particular, it is shown that
Grassmannians can be considered as generalized moduli spaces; this statement
permits us to define corresponding "string amplitudes" (at least formally). One
can conjecture, that it is possible to explain the relation between
non-perturbative and perturbative string theory by means of localization
theorems for equivariant cohomology; this conjecture is based on the
characterization of moduli spaces, relevant to string theory, as sets
consisting of points with large stabilizers in certain groups acting on
Grassmannian. We describe an involution on the Grassmannian that could be
related to S-duality in string theory.
