pA single species of fly, iDrosophila melanogasteri, has been the subject of scientific research for more than one hundred years. Why does this tiny insect merit such intense scrutiny piDrosophilai's importance as a research organism began with its short life cycle, ability to reproduce in large numbers, and easy-to-see mutant phenotypes. Over time, laboratory investigation revealed surprising similarities between flies and other animals at the level of genes, gene networks, cell interactions, physiology, immunity, and behavior. Like humans, flies learn and remember, fight microbial infection, and slow down as they age. Scientists use iDrosophilai to investigate complex biological activities in a simple but intact living system. Fly research provides answers to some of the most challenging questions in biology and biomedicine, including how cells transmit signals and form ordered structures, how we can interpret the wealth of human genome data now available, and how we can develop effe