The chemokine CXCL12 (or SDF-1) and its receptor CXCR4 have originally been described as regulators of cell interactions in the immune system. However, over the past years it has become clear that this receptor/ligand pair is an important component of the machinery that controls cell migration in different regions of the developing nervous system. Here we will review some of these functions of the CXCL12/CXCR4 system, focusing on migration events in the cerebellum and the cortex. Furthermore, we will discuss these findings in light of the recently discovered second receptor for CXCL12, CXCR7, and the original functional properties of this molecule that have been described in zebrafish.