This is a multicentre, prospective, non interventional, non randomized, open label study for the assessment of the adherence to therapy with Rebif of subjects with RRMS. The participating subjects shall be already on treatment with (Rebif) prior to their enrolment into the study, according to the approved Summary of Product Characteristics (SPC) and the clinical, imaging and laboratory findings of the disease, as evaluated by their treating physician, in real life clinical practice. Data will be collected retrospectively from a sample of 150 subjects' medical files and through questions that will be posed to the subjects, and prospectively during the course of the study. The total duration of the study is estimated to be 18 months.