The possibility that cells of multicellular organisms may compete with one another has been postulated several times. It was experimentally confirmed in Drosophila, probably for the first time, when cells with different metabolic rates were mixed: cells that would have been viable on their own disappeared due to the presence of metabolically more active cells. After almost 30 years of neglect, genetic analysis in Drosophila has started to reveal a gene network that regulates the competitive behavior of cells. If the genes regulating cellular competitiveness in Drosophila have a conserved function in mammals, the study of cell competition could have an impact in several biomedical fields, including functional degeneration, cancer, or stem cell therapies.