The proper functioning of the nervous system relies on the establishment of precise neuronal circuits. These neuronal circuits are largely formed during early development. To form functional neuronal circuits, neurons receive specific information in the form of extracellular cues from the target tissues that they innervate. The family of neurotrophins provides one of the best examples of these target-derived instructive cues that regulate diverse developmental events in the vertebrate nervous system, including survival, axonal and dendritic growth and synapse formation. Using a combination of cell biological, biochemical and imaging techniques as well as mouse genetics, we are investigating: (1) how neurotrophic factors coordinate neuronal development by regulating the neuronal endocytic machinery, and (2) growth factor signaling pathways underlying axonal growth, morphology and innervation of target tissues during development.