The Drosophila larva has an antennal lobe with an overall structure similar to all other insects – olfactory receptor neurons that express specific odor receptors, local interneurons that integrate information across glomeruli, and projection neurons that innervate higher brain areas – but also has remarkable numerical simplicity and virtually no cellular redundancy. The small size of its antennal lobe has allowed we and others to reconstruct its complete wiring diagram. The animal’s optical transparency combined with the powerful genetics afforded by Drosophila allows us to dissect the computational dynamics of the antennal lobe using optogenetics and optical neurophysiology. I will discuss our efforts to unravel information processing in this small sensory circuit at the structural, functional, and behavioral levels.