Under extreme conditions the mechanical or electrical properties of solids tend to be destabilized and failure or breakdown occurs. In practice these instabilities in the solid often nucleate or spread from disorders in the structure of the solid. This book investigates the modelling of such failure and breakdown processes. The basic principles are illuminated with a large number of computer simulations and laboratory simulations or `table top' experiments. Three particular case studies of failure are presented: electrical failures like fuse and dielectric breakdown; mechanical fracture; and earthquakes as an example of dynamic failure.