This book is a report of a four-day Symposium on the Biochemistry and Physiology of Visual Pigments, which took place immediately after the VIth International Congress on Photobiology, held in Bochum, Federal Republic of Germany, in August 1972. This meeting, which brought together about 50 investigators of various aspects of the visual process, was devoted to the visual cells of both vertebrates and invertebrates. Whereas the International Symposium on the Biochemistry of the Retina, held at Nij­ megen, The Netherlands, in 1968, had concentrated on vertebrate photoreceptors, this Symposium dealt with invertebrate photoreceptors as well, so that workers in each field could become acquainted with recent progress in the other area. The papers presented at the Symposium were divided into six main topics, to each of which a half-day session was devoted. The six parts of this book, following the intro­ ductory lecture, essentially correspond to these sessions. In addition to the invited con­ tributions, the volume contains a number of short communications by other partici­ pants and two contributions by invited participants, who were unable to attend. The volume closes, as did the Symposium, with a General Discussion, prepared and moderated by S. L. BONTING, in which an attempt was made to integrate various new findings, and to reconcile certain points of disagreement.