String theory is a framework to build models of quantum gravity.This relates quantum gravity in a spacetime that asymptotes to anti-de Sitter space with an ordinary quantum field theory that lives in one lower dimension, and has a symmetry under angle-preserving (conformal) transformations.

This is interesting because it provides us with a non-perturbative definition of quantum gravity, in a setup that is rich enough to permit black holes, non-trivial scattering, and is related to cosmological models.