These proceedings are based on lectures given at the Les Houches summer school in 1986. These lecture notes contain a wealth of information on diverse topics, such as classical percolation, localization, growth processes and pattern formation, spin glasses and related complex systems, and macroscopic quantum phenomena. Each of these subjects could easily fill an entire volume, but the summer shool was relatively wide-ranging in the topics that were covered. The lecturers on each topic were quite well chosen, their notes uniformly informative, and the generous references in most of the articles can lead the dedicated reader deeper into a single field. This volume should therefore serve as a valuable reference for both the uninitiated and the expert alike.