We are at the beginning of an exciting new era for neuroscience, as our ability to probe neural circuits and their neuronal components is advancing rapidly due to genetic and optogenetic tools. Our research program applies these tools to address fundamental questions about how the same neural circuitry generates different motor patterns, and how such circuits develop and are maintained. We investigate these questions using the Drosophila larva, which has the following advantages:(i) The connectome of the larval motor circuit is near completion, enabling us to identify, at the single-synapse level, the pre and postsynaptic partners of each individual neuron embedded in it. This anatomical map has provided an excellent substrate to study the development, maintenance, and function of larval motor circuits as well as the cell biology of individual neurons embedded within it. (ii) The larval CNS generates multiple motor behaviors that can be studied at the single neuron/single muscle level. Moreover, using the modern optogenetic methods, it is possible to access individual neurons, monitor or alter their activity, and observe the behavioral consequences. (iii) It is also feasible to selectively inactivate or induce ectopic expression of any gene (e.g. those coding for transcription factors) in the neuron of interest, and examine its effect on intrinsic neural properties, morphology, connectivity pattern, and behavioral performance of the animal, thereby linking the gene to development and behavior.