  The problem of motion in General Relativity has lost its academic status and
become an active research area since the next generation of gravity wave
detectors will rely upon its solution. Here we will show, within scalar
gravity, how ideas borrowed from Quantum Field Theory can be used to solve the
problem of motion in a systematic fashion. We will concentrate in
Post-Newtonian corrections. We will calculate the Einstein-Infeld-Hoffmann
action and show how a systematic perturbative expansion puts strong constraints
on the couplings of non-derivative interactions in the theory.
