MicroRNAs (miRNAs), a class of small, non-protein-coding transcripts about 21 nucleotides long, have recently entered center stage in the study of posttranscriptional gene regulation. They are now thought to be involved in the control of about one third of all protein-coding genes and play a role in the majority of cellular processes that have been studied. We focus on the role of the miRNA pathway in brain development, function, and disease by highlighting recent observations with respect to miRNA-mediated gene regulation in neuronal differentiation, synaptic plasticity, and the circadian clock. We also discuss the implications of these findings with respect to the involvement of miRNAs in the etiopathology of brain disorders and pinpoint the emerging therapeutic potential of miRNAs for the treatment of human diseases.