Microglia or microglial cells are a type of neuroglia (glial cells) located in the brain and spinal cord. Microglia are cells of mesodermal/mesenchymal origin that migrate into the central nervous system to become resident macrophages in the unique brain microenvironment. Microglia is ontogenically distinct from other phagocytic cells of the mononuclear phagocytic system such as dendritic cells, macrophages and monocytes. Microglia are highly dynamic cells that interact with neurons and non-neuronal cells.

Microglia respond to pathogens and injury by changing their morphology and migrating to the site of infection or injury, where they destroy pathogens and eliminate damaged cells. As part of their response, they secrete cytokines, chemokines, prostaglandins and reactive oxygen species, which help direct the immune response. In addition, they play a key role in the resolution of the inflammatory response, through the production of anti-inflammatory cytokines. Microglia have also been widely studied for their detrimental role in neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, as well as heart disease, glaucoma and viral and bacterial infections.