In this volume, six review articles which cover a broad range of topics of current interest in modern optics are included.

The first article by S. Saltiel, A.A. Sukhorukov and Y.S. Kivshar presents an overview of various types of parametric interactions in nonlinear optics which are associated with simultaneous phase-matching of several optical processes in quadratic non-linear media, the so-called multi-step parametric interactions.
The second article by H.E. Tureci, H.G.L. Schwefel, Ph. Jacquod and A.D. Stone reviews the progress that has been made in recent years in the understanding of modes in wave-chaotic systems.
The next article by C.P. Search and P. Meystre reviews some important recent developments in non-linear optics and in quantum optics.
The fourth article by E. Hasman, G. Biener, A. Niv and V. Kleiner discusses space-variant polarization manipulation. The article reviews both theoretical analysis and experimental techniques.
The article which follows, by A.S. Desyatnikov, L. Torner and Y.S. Kivshar presents an overview of recent researches on optical vortices and phase singularities of electromagnetic waves in different types of non-linear media, with emphasis on the properties of vortex solitons. The concluding article by K. Iwata presents a review of imaging techniques with X-rays and visible light in which phase of the radiation that penetrates through a transparent object plays an important part.