Whether it's a dentist's drill or a tunnel drill, an automobile assembly line or a CD player, somewhere in the course of its development, a mechanical engineer has had a hand in its design. Mechanical engineers design, develop and build an enormous range of technical systems and mechanisms for industry and consumers. They have an important hand as well in stimulating the development of bio-systems, and micro- and nano-scale devices. Innovations in these areas are of vital importance in efforts to reduce energy consumption, to ease pressures on the environment, and to build a more sustainable society.