Microglia, one of the glial cell types in the central nervous system (CNS), is an important integral component of the neuro-glial cell network. Microglia play an important role in brain immune surveillance. They can present antigens in the molecular context of MHC class II expression to CD-4 positive T cells, and are capable of Fc-mediated phagocytosis, and share many common antigens with hemopoietic and tissue macrophages. Upon activation, they act as brain macrophages to clear tissue debris damaged cells, or microbes; when programmed cell death occurs during brain development or when the CNS is injured. Furthermore, there is evidence that microglia are important in a variety of physiological and pathological processes in the brain; through interaction with neurons, other glial cells, and production of biologically active substances such as growth factors and cytokines. Rat Microglia provide an invaluable tool for understanding physiological and pathophysiological relevance in brain function and disease.