The central nervous system (CNS) hosts a variety of immune cells including two anatomically and transcriptionally distinct macrophage populations: microglia are found in the parenchyma, whereas CNS border-associated macrophages (CAMs) cover the CNS interfaces, such as the perivascular spaces and the meninges. Recent studies have given novel insights into the origins, kinetics, functions, transcriptomic profiles, heterogeneity of microglia and CAMs. In this symposium, I will discuss our current knowledge of the ontogenetic relationship and the mechanism for the establishment of these CNS macrophages during development.