Dedicated to the physics of processes in the generators of the second optical harmonics (with non-resonator and intra-resonator generation) and parametric light generators . The latest directions and achievements in the development of these generators are reflected; optical circuits used in practice are considered. The systematizations describe different approaches and methods of calculation, taking into account a combination of factors , real impact on the operation of the generators under consideration (aperture effects,) focusing radiation, Inhomogeneity of birefringence , Self-inflicted heat , photorefractive effect, Multi-frequency pumping, etc.. ). The book is a continuation of the monograph L. In. Tarasova (, 1981). For scientists and engineers working in the field of laser technology, nonlinear optics and related fields; can also be used by teachers and students of universities, graduate students .