Cells in developing tissues are directed to their appropriate differentiation fate by signals they receive from other cells. A key goal is to understand the mechanisms by which cells produce and release the signals and the processes by which other cells receive and interpret those signals. We examine these processes in the developing fruit fly in both neural and non-neural tissues. The retina is ideally suited for the study of short range signaling, and our investigations focus on how specific photoreceptor cell fates are directed by the intercellular signaling mechanisms. We are also investigating long-range signaling mechanism that direct developmental behavior of cells, both in the retina and in non-neural tissues such as the wing and leg.