  In this chapter, we will review the field-theoretic treatment of General
Relativity based on an effective field theory extension of the Einstein-Hilbert
action. This pragmatic route to low-energy quantum effects in gravity
critically underpins miscellaneous investigations of phenomenological and
quantum extensions of General Relativity. We discuss how it allows quantum
field theory to be a theoretical laboratory for testing Einstein's theory of
gravity and demonstrate the current state of the art of an efficient and
practical scheme for evaluating the classical components of perturbative
weak-field scattering amplitudes until the fourth post-Minkowskian order. Such
results complement numerical predictions in Einstein's theory of gravity.
