This book is written for our friends in Germany and abroad to give an account of our main interests during the last years. We gratefully take the opportunity provided by Springer Verlag with the Series Studies of Brain Function to present some of our recent work on vision in Drosophila in a coherent form and in a broader context than publications in periodicals would permit. We want to picture the visual system of the fly fitting it into the natural history from which our own vision emerged. In this perspective genetics seems to be a useful ap- proach. Our study is a rather personal exercise. We have neither the expertise nor the ambition to cover the whole literature or to compile- all the knowledge about vision in flies. We are not even in a position to present, with the appropriate weight and breadth, the pioneering contributions of those who established this field of research. Our account mirrors our own intersects. We are selecting and interpreting other peoples’ work from this subjective point of view, although we try to present it in its own right. For several years we have been fascinated by the first glimpses of the inner life of an insect and we hope to convey this fascination to those who are not discouraged by the scien- tific procedure.