LQG is, along with string theory, one of the best-established quantum gravity programs. Proponents of LQG hold that the most important lesson of GR is the diffeomorphism invariance of the gravitational field, and thus seek to preserve diffeomorphism invariance at the high-energy level of quantum gravity. Like the discrete approaches to quantum gravity discussed in the previous chapter, LQG is non-perturbative and researchers in LQG suggest that the problems with perturbative approaches (i.e. the problems associated with the non-renormalisability of gravity) may be a consequence of the failure of perturbation theory when applied at the scales being considered.