Neurotransmission requires proper organization of synaptic vesicle pools and rapid release of vesicle contents upon presynaptic depolarization. Genetic studies have begun to reveal a critical role for scaffolding proteins in such processes. Mutations in genes encoding components of the highly conserved MALS/CASK/Mint-1 complex cause presynaptic defects. In all three mutants, neurotransmitter release is reduced in a manner consistent with aberrant vesicle cycling to the readily releasable pool. Recently, liprin-alpha proteins, which define active zone size and morphology, were found to associate with MALS/CASK, suggesting that this complex links the presynaptic release machinery to the active zone, thereby regulating neurotransmitter release.