Release of neurotransmitters by synaptic vesicles is central to synaptic transmission. The mechanisms by which these vesicles are filled, release their contents into the synapse and ultimately are recycled are important examples of membrane trafficking. Despite intensive research, however, the roles of the key players in the synaptic vesicle cycle - SNAREs, the Rab3 GTPase, vacuolar H+ ATPases (V-ATPases) and the SNARE-binding protein UNC-18 - remain controversial. In Cell Science at a Glance (p. 3661 + poster), Robby Weimer and Erik Jorgensen survey current models for the functions of these proteins in priming, docking, fusion and recycling of synaptic vesicles, summarising the evidence for their involvement at each stage.