This minicourse contains a description of recent results on the modelling of rarefied gases in weakly non equilibrium regimes, and the numerical methods used to approximate the resulting equations. Therefore this work focuses on BGK type approximations, rather than on full Boltzmann models. Within this framework, models for polyatomic gases and for mixtures will be considered. We will also address numerical issues characteristic of the difficulties one encounters when integrating kinetic equations. In particular, we will consider asymptotic preserving schemes, which are designed to approximate equilibrium solutions, without resolving the fast scales of the approach to equilibrium.Kinetic theory was initially developed to study the behaviour of rarefied gases, with applications, as a typical example, to flow in the higher levels of the atmosphere. Recently its scope has enlarged to include many non equilibrium phenomena, arising, for instance, in the study of microfluids, i.e. flows occurring in domains with microscales, where the equilibrium hypothesis underlying classical gas dynamics does not hold. But kinetic models have also been successfully applied to phenomena which do not stem from fluid dynamics. The attractive feature of kinetic theory beyond gas dynamics is its ability to start from the characteristics of interactions of particles at a microscopic scale, to develop equations for the collective behaviour. These new applications include social sciences, see the examples in [54] or natural sciences [8], or even traffic flow, [40]. For a short introduction to rarefied gas dynamics see [23][Chapt. 1]. A more in depth text is [22] This paper will review kinetic models of BGK type, and the numerical techniques which permit to obtain accurate and reliable approximate solutions. TheThe collisions conserve mass, momentum and energy, which, at the microscopic level, means