Multiple sclerosis is a major demyelinating disease of the central nervous system. It has a significant economic and social impact. Its etiology is unclear, although there are several hypotheses, such as infections or genetics. In its pathophysiology, it seems that immune activation attacks the myelin sheath, causing a progressive and irreversible axonal degeneration. The disease produces a variety of symptoms, and diagnosis requires fulfilling a number of criteria and the exclusion of other possible causes. The role of neuroimaging is very important, especially Magnetic Resonance Imaging. Despite the availability of disease-modifying drugs, none of them are able to halt its progress, and the most useful drugs are those designed to alleviate the symptoms of outbreaks. Overall, multiple sclerosis requires a significant effort in research to clarify not only why and how it occurs, as well as the development of new measures to improve quality of life of affected patients.