Observations of gravitational waves from inspiraling compact binary systems allow us not only to measure the astrophysical properties of these systems but also to test gravity in its strong field regime. Both the detection and analysis of gravitational waves require a bank of very accurate template gravitational waveforms. In order to constrain deviations from general relativity, one also has to build template waveforms for alternative theories of gravity.

In this talk, I will focus on massless scalar-tensor theories and address the question of the dynamics and gravitational radiation of non-spinning compact binaries. In particular, I will present our method, based on a Fokker action adapted to the specificities of scalar-tensor theories. It allows us to derive the equations of motion at the 3PN order in harmonic coordinates. This result is crucial in order to compute the scalar and gravitational waveforms at 2PN order. I will conclude by a short discussion on tidal effects, that are expected to start at 3PN in scalar-tensor theories.