Many molecules enter the cell interior within clathrin-coated vesicles, in process termed endocytosis. This process is critical to the way we move and think. At the tip of each axon, synaptic vesicles (packages of neurotransmitter) release their contents when the nerve is stimulated by fusing with the cell surface. Almost instantly, the membrane of the synaptic vesicle is then retrieved within clathrin-coated vesicles. Endocytosis is thus tightly coupled to exocytosis, the stimulated release of neurotransmitter. Failure to recover synaptic-vesicle membrane results in both morphological disruption of the nerve terminal and defective neurotransmission. We study the mechanisms and molecules involved in clathrin-coat assembly. To understand how these complex structures assemble within only a minute or two, we use biochemical, cell biological and structural approaches to unravel the protein-protein interactions that orchestrate the formation of this elaborate protein-sorting machine.