Perturbative Approaches to Nonperturbative Quantum Gravity

We discuss the birth of the nonperturbative approach to quantum gravity known as quantum Einstein gravity, in which the gravitational interactions are conjectured to be asymptotically safe. The interactions are assumed to be finite and consistent at high energies, thanks to a scale-invariant ultraviolet completion. We present the framework on the basis of perturbative arguments that originally motivated it, paying special attention to the ε-expansion in d = 2 + ε dimensions and the large-N expansion for N the number of flavors of matter fields. The chapter is organized in such a way that each section is mostly independent and can offer several ideas for both conceptual and technical future developments.