Electronic excitation is a means to change materials properties. This book analyses the important features of the changes induced by electronic excitation, identifies what is critical, and provides a basis from which materials modification can be developed successfully. Electronic excitation by lasers or electron beams can change the properties of materials. In the last few years, there has been a mix of basic science, of new laser and electron beam tools, and of new needs from microelectronics, photonics and nanotechnology. This book extends and synthesises the science, addressing ideas like energy localisation and charge localisation, with detailed comparisons of experiment and theory. It also identifies the ways this understanding links to technological needs, like selective removal of material, controlled changes, altering the balance between process steps, and possibilities of quantum control. This book will be of particular interest to research workers in physics, chemistry, electronic engineering and materials science.