Because almost everything we know about Drosophila phototransduction has come from studies based on genetic approaches, this review begins with a discussion of genetic approaches. We then present a brief overview of Drosophila phototransduction (section on Drosophila phototransduction: an overview) followed by a more detailed treatment of individual components of the transduction machinery (section on Components of the phototransduction machinery). Discussion of transduction mechanisms is presented under three headings: Mechanism(s) of channel excitation, Organization of the transduction proteins, and Regulatory mechanisms in phototransduction. Perhaps the most important unanswered question in this field is the mechanism(s) of activation and regulation of transduction channels. This question is explored in the section entitled Mechanism(s) of channel excitation. Identification of at least two of the proteins discussed was totally unexpected: the rhodopsin chaperone protein, ninaA, and the signal complex scaffold protein, INAD. They are discussed in the sections titled Requirement for a chaperone protein for Rh1 opsin, and: Formation of signaling complexes, respectively. One of the important developments in this field has been the discovery of mammalian homologs of many of the proteins identified in Drosophila. A brief discussion of the most extensively studied of these, the mammalian homologs of light-activated channel protein, trp, is presented in the section on Mammalian Homologs of trp. We conclude the review with Perspective, a brief look at the current status and the future outlook of the field.