This volume contains six review articles dealing with topics of current research interest in optics and in related fields. The first article deals with the so-called embedding method, which has found useful applications in the study of wave propagation in random media. The second article presents a review of an interesting class of non-linear optical phenomena which have their origin in the dependence of the complex dielectric constant of some media on the light intensity. These phenomena which include self-focusing, self-trapping and self-modulation have found many applications, for example in fibre optics devices, signal processing and computer technology. The next article is concerned with gap solitons which are electromagnetic field structures which can exist in nonlinear media that have periodic variation in their linear optical properties, with periodicities of the order of the wavelength of light. Both qualitative and quantitative descriptions of gap solitons are presented and some experimental schemes for their detection in the laboratory are discussed. The fourth article describes methods for the determination of optical phase from phase-modulated images. These methods have found applications in plasma diagnostics, in connection with flow characterisation and in the design of new optical instruments. The final article reviews developments relating to imaging, through turbulence in the atmosphere. It looks at the state-of-the-art of our understanding of this subject and discusses the most important methods that are presently employed to compensate for image distortion caused by atmospheric turbulence.