The project is devoted to a review of some manifastations of the nonlinear optics phenomena.rnIn the rst chapter of this project, we will see the brief introduction of nonlinear opticsrnlike nonlinear optical phenomena,nonlinear optical material and thier properties,polarization ofrnnonlinear optics and thier wave equation. The second chapter of this project deal with physicalrnorigin of NLO phenomena and futurity of NLO. chapter three of this project about opticallyrninduced bistability and Chapter four is about thier application of NLO