Laser physics has always been driven by a genuinely scientific quest to extend existing limits, limits of physical knowledge and limits of physical methods. Enhancing precision, sensitivity, and resolution has been an essential topic of this evolution. Experiments and concepts of laser physics have also earned a central place in modern physics. More than 100 years after the invention of quantum physics, subtleties of light-matter interaction can be beautifully illustrated through the application of lasers, an invaluable highlight of our current presentation of modern microscopic physics. The scientific advancement of physics is impossible without the ingenuity of experimenters and of theoreticians. Among those, Theodor Hänsch has oc­ cupied a commanding position for many decades now, contributing numerous original and fundamental contributions to the field of laser physics. This vol­ urne was thus initiated on the occasion of his 60th birthday. It demonstrates the influence of his scientific activities at present and during the recent past. Current developments in fields such as atomic elocks, precision measurements of fundamental constants, nonlinear optical effects, Bose-Einstein condensa­ tion, and atomic quantum engineering underline the virtue of concepts and results derived in his laboratories.