This book has been designed as a tutorial for the theory of non-linear waves in optics. The emphasis is on the basic aspects of the theory, on analytical methods and on non-dissipative phenomena. The self-induced transparency phenomenon and short pulse propagation in fibres are good examples of the important role solitons play in non-linear optics. The classical problem of non-linear optics is the parametric interaction of waves. Three- and four-wave parametric interaction processes are of particular interest because they enable new applications of the inverse scattering transform method to...