The primary tool for investigating the gravitational RG flow with respect to the energy scale k at the nonperturbative level is the effective average action Γ Γ k for gravity. It is the scale dependent version of the effective action where in the underlying functional integral field modes with covariant momenta below k are suppressed while only the remaining are integrated out. For a given theory space, let Φ Φ and Φ Φ ¯ ¯ denote the set of dynamical and background fields, respectively. Then Γ Γ k satisfies the following Wetterich–Morris-type functional RG equation (FRGE):