  In this review the problem of statistical description of isolated quantum
systems of interacting particles is discussed. Main attention is paid to a
recently developed approach which is based on chaotic properties of compound
states in the basis of non-interacting particles. In order to demonstrate the
most important aspects of this approach, the matrix model of two-body random
interaction between Fermi-particles has been used. Different problems have been
considered such as the onset of chaos and statistical equilibrium, the relation
between the structure of eigenstates and distribution of occupation numbers,
the emergence of the Fermi-Dirac distribution in isolated systems of finite
number of particles and many others. The application of the approach to
dynamical systems with the classical limit is discussed as well.
