The course is devoted to mathematical problems of classical statistical mechanics. The main focus will be on the large time behavior of particle ensembles (gases). The physical processes observed in such systems are well-known to be the approach to equilibrium and scattering at infinity. The mathematical justification for the corresponding picture has been found only recently in the works of C. Villani. It is supposed to give an introduction in the modern operator theory methods that allow to analyse the approach to equilibrium (hypocoercitivity) and the large time behavior of the systems in the scattering regime (functional models)