Mechanisms of input and output synaptic specificity: finding partners, building synapses, and fine-tuning communication

•Cell adhesion systems are critical determinants of synaptic specificity.•Neuroligins and FGFs contribute to the balance of inhibitory to excitatory synapses.•Synaptic plasticity mechanisms can differ for different synaptic inputs and outputs.•New tools are advancing our molecular understanding of synaptic specificity.