  The paper is a brief review of the works devoted to problem of effective
action in N=2 super Yang-Mills theories in harmonic superspace approach. The
formulation of N=2 superfield models in harmonic superspace is discussed,
background field method for N=2 super Yang-Mills theory is constructed and
general structure of effective action in harmonic superspace is investigated.
It is shown how the holomorphic and non-holomorphic contributions to effective
action can be calculated within the harmonic superspace approach.
