Most of our current knowledge of olfactory associative learning in Drosophila comes from the behavioral and molecular analysis of mutants that fail to learn. The identities of the genes affected in these mutants implicate new signaling pathways as mediators of associative learning. The expression patterns of these genes provide insight into the neuroanatomical areas that underlie learning. In recent years, there have been great strides in understanding the molecular and neuroanatomical basis for olfaction in insects. It is now clear that much of the association between the conditioned stimuli and the unconditioned stimuli in olfactory learning occurs within mushroom bodies — third order olfactory neurons within the central brain. In this review, we discuss the nature of the behavioral tasks, the molecules, and the neuronal circuits involved in olfactory learning in Drosophila. BioEssays 23:571–581, 2001. © 2001 John Wiley & Sons, Inc.