In this report we review the most important concepts in statistical physics of polymer networks. We present the field theoretical approach to the theory of phantom networks and discuss main applications of this approach to calculate the scattering spectra of weakly charged, randomly cross-linked polymer gels. We study the phenomenon of microphase separation in the model of cross-linked block copolymer. The main models of topological entanglements in polymer networks are reviewed and a new Slip-Tube Model for nonlinear elasticity of entangled polymer networks is proposed. ©2000 American Institute of Physics.