Multiple sclerosis (MS) is a debilitating autoimmune disease characterized by both inflammation and axonal degeneration. The resulting demyelination and subsequent degeneration of axons account for the disability of patients with MS. Early investigations indicated that disease progression was driven by CD4(+) effector T cells. However, clinical therapies specifically targeting these cells have, for the most part, not been effective. Therefore, new areas of research in experimental autoimmune encephalomyelitis (the experimental model of MS) and human MS have identified previously unknown contributions to disease pathogenesis, including interleukin-17-producing T helper 17 cells, B cells, CD8(+) T cells, and both CD4(+) and CD8(+) T-regulatory cells. Research into the respective mechanisms of action of these cells has identified novel therapeutic targets to combat this devastating disease. This article reviews the autoimmune response in patients with MS compared with individuals without MS and summarizes the fundamental differences in the immunologic response between people with and without MS. Investigations into these autoimmune differences and the disruption of the homeostatic balance of the immune system will help guide future research into MS therapeutics, with particular attention to the long-term management of this disease.