Topological amplitudes in string theory

We show that certain type II string amplitudes at genus g are given by the topological partition function F_g discussed recently by Bershadsky, Cecotti, Ooguri and Vafa. These amplitudes give rise to a term in the four-dimensional effective action of the form Σ_gF_gW^{2 g}, where W is the chiral superfield of N = 2 supergravitational multiplet. The holomorphic anomaly of F_g is related to non-localities of the effective action due to the propagation of massless states. This result generalizes the holomorphic anomaly of the one loop case which is known to lead to non-harmonic gravitational couplings.