Background Field Method and Structure of Effective Action in N=2 Super   Yang-Mills Theories
  This paper is a brief review of background field method and some of its applications in N=2 super Yang-Mills theories with a matter within harmonic superspace approach. A general structure of effective action is discussed, an absence of two-loop quantum corrections to first non-leading term in effective action is proved and N=2 non-renormalization theorem in this approach is considered. 
I.L. Buchbinder (Tomsk State Pedagogical University), B.A.Ovrut   (University of Pennsylvania)