We review in this article some issues related to multi-timescales for the numerical modeling of atmospheric chemical kinetics. There is indeed a wide range of characteristic timescales for atmospheric chemistry and the time evolution is characterized by a slow-fast behaviour. We present here some related points: the use of appropriate stiff solvers (numerical point of view), the existence of an underlying reduced model (the counterpart for modeling) and some by-products for other aspects of numerical modeling (e.g. splitting methods and adjoint modeling).