A key ingredient in extracting cosmological information from galaxy surveys is to link the distribution of discrete Large-Scale Structure tracers (such as galaxies) to that of the underlying continuous dark matter field. This is achieved through the so-called bias formalism. After motivating and introducing in details this formalism, I will present two different techniques to measure the parameters entering the model (the bias parameters) up to third order: separate universe simulations and the tree-level trispectrum. I will present some of the most precise measurements to date for several bias parameters, obtained using gravity only numerical simulations, and comment on them.