A collection of Bogolubov's papers on dynamical theory, which introduce the key concept of the hierarchy of relaxation times in statistical physics. A method of obtaining a system of coupled equations for the probability densities for groups of one or more particles is proposed. This has proved to be the most effective method in statistical mechanics for equilibrium and non-equilibrium to date. In his papers, Bogolubov clarifies how stochastic behaviour, which is specific for a macroscopic description, arises in a purely mechanistic approach, in which microscopic equations of dynamical theory are used.