This volume originated in a happy event honoring Arthur Schawlow on his 65th birthday. As a research physicist, Schawlow has been a major infiuence on the present nature of physics and of high technology. He has also had a role, through the American Physical Society and other organizations, in shaping policy for the world of physicists. Important as these professional activities have been, the contributions to this volume were not prepared just for these reasons, but more for Art Schawlow the friend, colleague, and teacher. I am one who has had the privilege of knowing and collaborating with Art, probably over a longer period of time than others participating in this volume, and in a number of different enterprises; his friendship and stimulating scientific abilities are a very significant part of my own life. It is hence a pleasure to take part in this volume celebrating his contributions to science and to scientists. Schawlow's career has been geographically centered at the University of Toronto, Columbia University, the Bell Telephone Laboratories, and Stan­ ford University. But, as is illustrated by the papers of this volume, its effects and his personal infiuence have diffused widely. In his own work, Art Schawlow is noted for thoughtful imagination, keen physical intuition, and what might be thought an interest in gadgets - not just any gadgets, but beautiful and innovative mechanisms or new techniques in which he charac­ teristically recognizes important potentials.