The paper discusses the possibility of a massless dilaton in string theory and its implications for cosmology. The authors argue that non-perturbative string loop effects can reconcile the existence of a massless dilaton with experimental data if the dilaton coupling functions exhibit universality. They show that the cosmological evolution of the graviton-dilaton-matter system naturally drives the dilaton towards values where it decouples from matter, a phenomenon they call the "Least Coupling Principle." This mechanism is efficient enough to satisfy current experimental constraints on the dilaton's coupling to matter. The authors provide quantitative estimates of the residual deviation from general relativity at the present cosmological epoch, particularly for violations of the equivalence principle. They conclude that the weakly coupled massless dilaton could lead to observable deviations from general relativity, motivating further experimental tests of Einstein's Equivalence Principle.The paper discusses the possibility of a massless dilaton in string theory and its implications for cosmology. The authors argue that non-perturbative string loop effects can reconcile the existence of a massless dilaton with experimental data if the dilaton coupling functions exhibit universality. They show that the cosmological evolution of the graviton-dilaton-matter system naturally drives the dilaton towards values where it decouples from matter, a phenomenon they call the "Least Coupling Principle." This mechanism is efficient enough to satisfy current experimental constraints on the dilaton's coupling to matter. The authors provide quantitative estimates of the residual deviation from general relativity at the present cosmological epoch, particularly for violations of the equivalence principle. They conclude that the weakly coupled massless dilaton could lead to observable deviations from general relativity, motivating further experimental tests of Einstein's Equivalence Principle.