[en] This review is devoted to the discussions of the parallels existing between four-dimensional gauge theories and two-dimensional sigma-models. Sigma-models are used as a laboratory allowing one to investigate such issues as the operator product expansion beyond perturbation theory, vacuum condensates, low energy theorems i.e. non-perturbative effects. The second part of the review represents a discussion of the supersymmetric 0(3) σ-model. The instanton-based method for calculating the exact Gell-Mann - Low function and fermionic condensate is considered in detail. Previously an analogue of this method has been used in four-dimensional Yang-Mills theories. The considered problems are: the instanton measure from purely classical analysis; a non-renormalisation theorem in self-dual external field; existence of vacuum condensates and their compatibility with supersymmetry