The discovery of gravitational waves by Advanced LIGO in 2015 and subsequent detections from binary black holes and a binary neutron star system have ushered in the era of gravitational wave astronomy. The modelling of compact object binary systems is thus of great urgency. Numerical relativity techniques are central to modelling the highly dynamical regime of the final stages of a binary coalescence. In this talk I will discuss several aspects of modelling such systems: in the first part I will focus on global quantities in binary black hole systems (energy and angular momentum), both in numerical relativity and semi-analytic models. In the second part, I will present some recent work on simulating compact object binaries that contain boson stars, self-gravitating collections of scalar fields which are potential black hole/neutron star mimickers.