Immune reactions in the brain, the most complex organ that directly or indirectly regulates almost every part of the body and its actions, need to be tightly regulated. Recent findings in the field of neuroimmunology have enhanced our understanding of immune cells not just inside the brain but also in adjacent tissues. Multiple types of immune cells exist and are active in neighboring border tissues, even in the steady state. In addition, advances in technology have allowed researchers to characterize a broad range of cell types, including stromal cells that support immune reactions. This review presents a short overview of the roles of the immune system in the brain during health and disease, with focus on adaptive immunity and anatomical sites of action. We also discuss potential roles of stromal cells.