The role of microglia in healthy brains is just beginning to receive notice. Recent studies have revealed that these phagocytic cells control the patterning and wiring of the developing central nervous system (CNS) by regulating, amongst many other processes, programmed cell death, activity-dependent synaptic pruning and synapse maturation. Microglia also play important roles in the mature brain and have demonstrated effects on behavior. Converging evidence from human and mouse studies together raise questions as to the role of microglia in disorders of brain development such as autism and, schizophrenia. In this review, we summarize a number of major findings regarding the role of microglia in brain development and highlight some key questions and avenues for future study. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease. (C) 2015 Elsevier B.V. All rights reserved.