MicroRNAs (miRNAs) are emerging as key modulators of post-transcriptional gene regulation in a plethora of tissues, including the nervous system. Recent evidence points to a widespread role for neural miRNAs at various stages of synaptic development, including dendritogenesis, synapse formation and synapse maturation. Furthermore, studies from invertebrates indicate that miRNAs might contribute to the control of synapse function and plasticity in the adult. Key features of synapse-relevant miRNAs include their ability to regulate mRNA translation locally in the synaptodendritic compartment and the modulation of their expression and function by neuronal activity. The potentially huge impact of miRNA-based mechanisms on higher-order processing, memory and neuropsychiatric disorders in vertebrates is just starting to be recognized.