  In these lectures I discuss peculiarities of the critical behaviour of
``non-ideal'' systems as it is explained by the renormalization group approach.
Examples considered here include account of the single-ion anisotropy,
structural disorder, frustrations. I introduce main ideas of renormalization
and show how it serves the explanation of typical features of criticality in
the above systems: softening of the phase transition, changes in the
universality class, complicated effective critical behaviour.
