The identification of microglial cells beyond cytomorphological criteria was facilitated by the development of staining procedures that take advantage of the exclusive expression of certain molecules in specific cell types (Table 1). The suitability of the various markers and methods is determined by the ability 1) to discriminate microglia from other CNS-resident cells, like neurons, astrocytes, oligodendrocytes, or endothelial cells; 2) to distinguish parenchymal microglia from other resident or infiltrating monocytes/macrophages; and 3) to either reveal the entire population of microglia or to display a bias for certain activity states.