This book describes modern focused ion beam microscopes and techniques and how they can be used to aid materials metrology and as tools for the fabrication of devices that in turn are used in many other aspects of fundamental metrology. Beginning with a description of the currently available instruments including the new addition to the field of plasma-based sources, it then gives an overview of ion solid interactions and how the different types of instrument can be applied. Chapters then describe how these machines can be applied to the field of materials science and device fabrication giving examples of recent and current activity in both these areas.