Several new treatments for multiple sclerosis (MS) have entered the market or are under development. The crucial question for the neurologist and person with MS now is the choice of the most appropriate treatment. To facilitate an informed decision, we will determine the mechanism of action of frequently used immunomodulatory treatments for MS and clarify especially the role of a subset of immune cells, the B cells, herein. Subsequently, we will investigate whether genetic factors can predict an individual’s response to treatment.