The presentation aims to give a brief review of several theoretical works carried out for layered superconductors [1-4]. It will be shown that the dependence of the transmission coefficient of nonlinear THz waves on the incident wave amplitude shows hysteretic behavior both when the waves are propagating along and across superconducting layers. The polarization transformation of incident waves after their reflection and transmission through a layered superconductor can occur. However, there exist two waves with mutually orthogonal polarizations, which practically do not interact with each other even in the nonlinear case. Using these two mutually orthogonal polarizations, we study polarization transformation of nonlinear transverse electric and transverse magnetic waves. In addition, we show that external magnetic field can be effectively used to control transparency and polarization transformation in layered superconductors.