Ellsworth Kelly's oeuvre can perhaps best be summed up by a phrase from Gottfried Boehm: "In between: this is the shortest formula of his aesthetics." With abstract expressionism at its peak, and based on the traditions of the abstract avant-garde in dialogue with color field painting, Kelly developed a vocabulary that left panel painting behind. In a conscious questioning of the conditions that underlie perception, he not only explores the relationships of painting and wall, sculpture and space, but also, and in particular, the relationship between viewer and work. A selection of more than 40 pieces of art from the past five decades, most of them from the collection of the artist, this book offers an expert investigation into the artistic development of one of the leading exponents of international postwar art.