This thesis is devoted to developing of an universal description of strongly interacting mesoscopic systems out of equilibrium. The nature of universalities we are looking for is twofold. Firstly, our goal is to find novel and simple dependences of physical observables on the experimental parameters. Secondly, we are looking for an universal theoretical approach that can be applied to a class of seemingly different strongly interacting physical problems. To achieve this generality, we rely on the bosonization technique, which allows one to account for interactions exactly. However, it is not trivial to apply this technique to out-of-equilibrium systems, because an injection of non-equilibrium electrons is naturally described at the fermion level, whereas the interactions are very elegantly incorporated within the bosonic framework. In this thesis, we discuss an approach that treats out-of-equilibrium corrections as perturbations. This allows us to stay within the framework of bosonization and to study non-equilibrium systems.