To understand the neural basis of chemotaxis requires an anatomical and functional understanding of the underlying circuit components- the individual neurons and how they interact with one another. The cellular anatomy at the first stages of odor processing is fairly well understood- odorants are detected at the periphery by olfactory receptor neurons (ORNs), which project to the primary olfactory processing center; the antennal lobe (AL). In the AL, ORNs make synapses with projection neurons (PN) which, in turn, send axons to the higher olfactory processing centers; the mushroom body (MB) and lateral horn (LH). During the last few years work in my lab has begun to describe the pathway underlying chemotaxis. We have identified a novel group of excitatory neurons, termed Odd neurons (so called because they express the transcription factor Odd-Skipped). The Odd neurons are an important link between higher olfactory processing centres and motor output systems and we can therefore use the Odd neurons as a starting point to trace the circuit involved in chemotaxis.