Nervous systems endow animals with cognition and behavior.To understand how nervous systems control behavior,neural circuits mediating distinct functions need to be identified and characterized.With superior genetic manipulability,Drosophila is a model organism at the leading edge of neural circuit analysis.We briefly introduce the state-of-the-art genetic tools that permit precise labeling of neurons and their interconnectivity and inves tigating what is happening in the brain of a behaving animal and manipulating neurons to determine how behaviors are affected.Brain-wide wiring diagrams,created by light and electron microscopy,bring neural circuit analysis to a new level and scale.Studies enabled by these tools advances our understanding of the nervous system in relation to cognition and behavior.