Microglia, the resident immune cells of the brain, have been shown to play crucial roles in normal brain development and adult physiology. This summary reviews findings from a 2011 Society for Neuroscience minisymposium on the role of microglia in the healthy brain. Microglia are dynamic and involved in synaptic pruning during postnatal development, adult neuronal plasticity, and circuit function. They actively remove extranumerary synapses through phagocytosis, a process mediated by the complement system. In the developing mouse retinogeniculate system, microglia engulf presynaptic retinal ganglion cell inputs during synaptic pruning, and this process is regulated by the complement receptor C3. Microglia also phagocytose apoptotic newborn neurons in the adult brain, a process essential for maintaining tissue homeostasis. Their interactions with synapses are influenced by neuronal activity, and they can modulate synaptic transmission through astrocytes. Microglia also participate in the remodeling of neuronal circuits, especially in response to experience. They are highly motile and their behavior is regulated by various factors, including neurotransmitters, chemokines, and ion channels. Microglia distribution and morphology vary across brain regions and are influenced by local cytoarchitecture. Overall, microglia are essential for normal brain function and their role in disease is increasingly recognized.Microglia, the resident immune cells of the brain, have been shown to play crucial roles in normal brain development and adult physiology. This summary reviews findings from a 2011 Society for Neuroscience minisymposium on the role of microglia in the healthy brain. Microglia are dynamic and involved in synaptic pruning during postnatal development, adult neuronal plasticity, and circuit function. They actively remove extranumerary synapses through phagocytosis, a process mediated by the complement system. In the developing mouse retinogeniculate system, microglia engulf presynaptic retinal ganglion cell inputs during synaptic pruning, and this process is regulated by the complement receptor C3. Microglia also phagocytose apoptotic newborn neurons in the adult brain, a process essential for maintaining tissue homeostasis. Their interactions with synapses are influenced by neuronal activity, and they can modulate synaptic transmission through astrocytes. Microglia also participate in the remodeling of neuronal circuits, especially in response to experience. They are highly motile and their behavior is regulated by various factors, including neurotransmitters, chemokines, and ion channels. Microglia distribution and morphology vary across brain regions and are influenced by local cytoarchitecture. Overall, microglia are essential for normal brain function and their role in disease is increasingly recognized.