In the present report the aspects of the investigation of various organic polymer semiconductors by using the high spectral resolution 2-mm waveband EPR technique accompanied by the method of steady-state saturation of spin-packets, the spin label and probe as well as saturation transfer ones are discussed. It reviews the original 2-mm EPR data concerned with a nature, relaxation and dynamics of paramagnetic centers delocalized on nonlinear charge carriers in various organic polymer semiconductors with different doping levels. The mechanism of charge transfer and its correlation with macromolecular dynamics in these polymers are discussed as well.