  We develop a field theoretical approach to the classical two-dimensional
models, particularly to 2D Ising model (2DIM) and $XYZ$ model, which is simple
to apply for calculation of various correlation functions. We calculate the
partition function of 2DIM and $XY$ model within the developed framework.
Determinant representation of spin-spin correlation functions is derived using
fermionic realization for the Boltzmann weights. The approach also allows
formulation of the partition function of 2DIM in the presence of an external
magnetic field.
