Microglia are the resident immune cells of the central nervous system, and accumulating data demonstrates a vast array of tasks in the healthy and injured brain. Microglia participate in both innate and adaptive immune responses. These cells contribute to the brain homeostasis, including the regulation of cell death, synapse elimination, neurogenesis, and neuronal surveillance. However, microglia can also become activated and/or deregulated in the context of neurodegenerative diseases, brain injuries, and cancer and thereby contribute to disease severity. As a consequence of these developments, microglia have attracted substantial attention on themselves.