Under extreme conditions the mechanical or electrical properties of solids tend to destabilize, leading to failure or breakdown. These instabilities often nucleate or spread from disorders in the structure of the solid. This book by two experts in the field investigates current techniques for modeling these failure and breakdown processes. It illustrates the basic modeling principles through a series of computer and laboratory simulations and `table top' experiments. The book centers on three important case studies: electrical failures like fuse and dielectric breakdown; mechanical fractures; and earthquakes, which exhibit dynamic failure. The material will interest all graduate students and researchers studying disordered systems, whether their focus is the mechanical failure of solids, the electrical breakdown of conductors, or earthquake mechanics.