T cells within the central nervous system (CNS) have been generally considered pathogenic, especially in the context of neuroinflammatory disease. However, recent findings have revealed varied functions for T cells in the healthy CNS, as well as more complex roles for these cells in infection and injury than previously appreciated. Here we review evidence indicating important roles for different T cell subsets in the maintenance of CNS homeostasis. We examine the contribution of T cells in limiting inflammation and damage upon CNS injury, infection, and in neurodegeneration, and discuss the current understanding of the cellular and molecular mechanisms involved. Insight into these processes will shed light on the adverse effects of T cell-depleting therapies and present inroads into new therapeutic approaches for treating diseases affecting the CNS.