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This book discusses the construction of analytical waveform models within the EOB formalism for a specific alternative theory of gravity, the so-called massless scalar-tensor theory. More specifically, authors describe the map of the dynamics of a binary system in scalar-tensor theory into the EOB formalism by building upon the PN expanded Lagrangian of the two-body problem at 3PN order. Authors discuss the generalization of the 2PN EOB Hamiltonian to 3PN order for the conservative part of the dynamics and then compute the scalar-tensor corrections to EOB potentials for generic orbits. Authors also compute the corrections in the EOB Hamiltonian due to tidal effects at 3PN order for circular orbits. Following this, authors describe the derivation of the angular momentum flux in the scalar-tensor theory for both the scalar part and the tensorial part up to 1PN and 1.5PN order, respectively. Authors then use these results along with the energy flux to compute generic orbit radiation reaction effects in the EOB formalism up to 1PN order. Finally, authors use the 3PN conservative dynamics results in the EOB formalism to derive the scattering angle in the scalar-tensor theories, which can be used in future as a check against the scattering angle computed using scattering amplitude techniques. Finally, authors implement up to 3PN conservative dynamics results in the EOB-based waveform model TEOBResumS. Additionally, authors investigate the improvement in the inference of the properties of neutron stars using the information of the observation of electromagnetic counterparts of the GW signal GW170817 and improved fits of the threshold mass. The application of the improved fits to the GW170817 signal implies that a significant part of the parameter space is not supported by the observation of the EM counterpart, implying improved constraints on the neutron star radii and hence the equation-of-state.