MicroRNAs play important roles in post-transcriptional regulation of gene expression by inhibiting protein translation and/or promoting mRNA degradation. Importantly, biogenesis of microRNAs displays specific temporal and spatial profiles in distinct cell and tissue types and hence affects a broad spectrum of biological functions in normal cell growth and tumor development. Recent discoveries have revealed sophisticated mechanisms that control microRNA production and homeostasis in response to developmental and extracellular signals. Moreover, a link between dysregulation of microRNAs and human brain disorders has become increasingly evident. In this review, we focus on recent advances in understanding the regulation of microRNA biogenesis and function in neuronal and glial development in the mammalian brain, and dysregulation of the microRNA pathway in neurodevelopmental and neurodegenerative diseases.