This Festschrift is a collection of essays contributed by students, colleagues and admirers of Charles Townes, who shared the Nobel Prize for Physics in 1964 for "fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the laser-maser principle." The contributions to this volume reflect Townes's wider interests and influence, ranging from quantum optics to astrophysics, and from electrical engineering to medicine. The broadly international character of the contributions reflects Townes's deep belief in the international character of science, as well as the breadth of the impact his work and teaching have had. The contributors include nine Nobel laureates. Arthur Shawlow provides the introductory biographical essay. Each of the chapters has been carefully edited to provide a consistency of presentation, while preserving the individuality of the authors.