Fundamental description of nonlinear optical phenomena in terms of higher order susceptibilities, quantum theory of nonlinear susceptibility, density matrix approach, rabi oscillations, optical bloch equations, Various specific nonlinear phenomena: electro-optic modulation, acousto-optic modulation, harmonic generation and frequency conversion, stimulated Raman and Brillouin scattering and amplification, parametric oscillation and amplification, self phase modulation, soliton propagation, and photorefractive effects, Applications to optical switching.