This book provides researchers at the forefront of nonlinear optical technologies with robust procedures and software for the investigation of the fundamental phenomena in nonlinear optical waveguide structures. A full vectorial electromagnetic formulation is adopted and the condition under which simplification to a scalar formulation is possible are clearly indicated. The need to model the dielectric saturation properly is identified and improved algorithms are presented for obtaining the complete power dispersion curve of structures exhibiting bistability. As the stability analysis of nonlinear modes is crucial to the developments of nonlinear model methods, an effective procedure to investigate the propagation of the scalar nonlinear waves in 3D is another important feature of the book. All of the procedures described as well as an automatic mesh generator for the finite element method are incorporated into a software package which is included with this book.