This is not a science book, nor even a book about science, although most of the contributors are scientists. It is a book of personal stories about Walter Kohn, a theoretical physicist and winner of half of the 1998 Nobel Prize in Chemistry. Walter Kohn originated and/or refined a number of very important theoretical approaches and concepts in solid-state physics. He is known in particular for Density-Functional Theory. This book represents a kind of "oral history" about him, gathered - in anticipation of his 80th birthday - from former students, collaborators, fellow-scientists, and friends.