Mounting evidence indicates that microRNAs (miRNAs) play important roles in the control of glial cell development in the central nervous system. Suppression of miRNA formation disrupts the initial generation of oligodendrocyte progenitor cells from the ventricular neuroprogenitor cells in the embryonic spinal cord. miRNAs also regulate the later events of oligodendrocyte development, including cell proliferation, maturation, and myelin formation. In addition, miRNAs are essential for the development of astrocytes, and inhibition of miRNA genesis completely blocks astrogliogenesis in the spinal cord.