This book contains contributions written by the world-leading scientists in high-resolution laser spectroscopy, quantum optics and laser physics. Emphasis is placed on precision related to results in a variety of fields, such as atomic clocks, frequency standards, and the measurement of physical constants in atomic physics. Furthermore, illustrations and engineering applications of the fundamentals of quantum mechanics are widely covered. It has contributions by Nobel prize winners Norman F. Ramsey, Steven Chu, and Carl E. Wieman and is dedicated to Theodor W. Hänsch on the occasion of his 60th birthday.