Applications of field theory methods in statistical physics of nonequilibrium systems This book formulates a unified approach to the description of many particle systems combining the methods of statistical physics and quantum field theory. The benefits of such an approach are in the description of phase transitions during the formation of new spatially inhomogeneous phases as well in describing quasi equilibrium systems with spatially inhomogeneous particle distributions (for example self gravitating systems) and metastable states. The validity of the methods used in the statistical description of many particle systems and models (theory of phase transitions included) is discussed and compared. The idea of using the quantum field theory approach and related topics (path integration saddle point and stationary phase methods Hubbard Stratonovich transformation mean field theory and functional integrals) is described in detail to facilitate further understanding and explore more applications. To some extent the book could be treated as a brief encyclopedia of methods applicable to the statistical description of spatially inhomogeneous equilibrium and metastable particle distributions. Additionally the general approach is not only formulated but also applied to solve various practically important problems (gravitating gas Coulomb like systems dusty plasmas thermodynamics of cellular structures non uniform dynamics of gravitating systems etc.)