This chapter discusses the role of dopamine in the fruit fly Drosophila melanogaster, a popular and genetically tractable invertebrate model organism with the largest complete adult brain connectome to date. Motivated behavior in the fly is directed by the mushroom body, a cerebellar-like network with many organizational and functional parallels to the vertebrate striatum. The mushroom body and striatum are both extensively innervated by reward-coding or punishment-coding dopaminergic neurons that send projections to distinct regions of each network. In both flies and mammals, dopaminergic neurons are highly heterogeneous, predominantly signal reward, and evoke similar signaling cascades through homologous receptors on target neurons. Research over the past 15 years has revealed, in unprecedented detail, how dopaminergic neurons targeting the mushroom body are organized into opponent systems that convey reward or punishment during associative learning, update memories when learned predictions are not met, and provide need-dependent motivational control. We propose that studying Drosophila may reveal similar principles of dopaminergic systems and maladaptive reward-seeking in mammals.