Oligodendrocytes are the myelin forming cells of the central nervous system. Over the last decade, their development in the embryonic brain and spinal cord has been documented following the discovery of early oligodendroglial markers. This review highlights the fundamental results obtained on the specification and migration of oligodendroglial cells and illustrates our advances in the knowledge of the cell lineage expressing plp (proteolipid protein), one of the early oligodendroglial genes.