Non-linear effects are basically manifested in a variety of physical phenomena such as defect mediated transitions, pattern formation, growth of aggregates, turbulence, chemical reactions, diffusion in porous media, biological information processing, etc. Many non-linear dynamical systems are extremely sensitive to small changes in the initial conditions. Different routes to chaos have been established and a new geometry, called fractal geometry, has been developed. The aim of this School is to review the main achievements of the modern theory of irregular structures and to discuss the exciting new trends in non-linear phenomena.