  We investigate the behaviour of a system of particles with the different
character of interaction. The approach makes it possible to describe systems of
interacting particles by statistical methods taking into account a spatial
nonhomogeneous distribution of particles, i.e. cluster formation. For these
clusters are evaluated: their size, the number of particles in a cluster, and
the temperature of phase transition to the cluster state. Three systems are
under consideration: electrons on the liquid helium surface, particles
interacting by the shielding Coulomb potential, which are found under the
influence of an elastic field (e.g. nucleons in a nucleus), and gravitating
masses with the Hubble expansion.
