This book examines the physical phenomena which occur when light from short-pulse lasers interacts with material in gaseous, liquid or solid forms. The huge concentration of photon energy within the laser ensures that ordinary matter is torn apart within a few cycles, giving way to a host of exotic physical effects such as multiphoton ionization, particle acceleration by plasma waves, relativistic self-channeling and high harmonic generation. These processes are central to a number of emerging applications of high-power laser technology, such as hadron therapy, X-ray flash-lamps and photonuclear physics.