This is an observational, international, multicenter study planned to be conducted in RMS subjects using the RebiSmart auto-injector at 300 sites in 15 countries across Europe. The participating countries are Austria, Belgium, Czech Republic, Denmark, Estonia, France, Germany, Hungary, Lithuania, Portugal, Slovakia, Sweden, Switzerland, the Netherlands and the United Kingdom. Subjects with RMS naïve to treatment or currently being treated with Rebif multi-dose injected by RebiSmart for no more than 6 weeks and meeting the eligibility criteria will receive Rebif 22 or 44 mcg subcutaneously three time a week. The dose of Rebif will be titrated during the initial four weeks of treatment. The planned observational period per subject is 12 months. The study visits comprises of: Baseline or Day 1 (Visit 1), Month 6 (Visit 2), and Month 12 (Visit 3).