Scientists use Drosophila 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 effective treatments for cancer, diabetes, and neurodegenerative diseases. Written by a leader in the Drosophila research community, First in Fly celebrates key insights uncovered by investigators using this model organism.