Disease modifying therapy (DMT) with one of the approved agents should be considered in all patients with active relapsing-remitting multiple sclerosis (RRMS) once the diagnosis of MS is confirmed and in selected patients with a clinically isolated demyelinating syndrome (CIS). Interferon beta modulates T-cell and B-cell function, decreases expression of matrix metalloproteinases reversing blood-brain barrier disruption, and alters expression of cytokines. A series of double-blind, placebo-controlled Phase 3 trials in RRMS supported the benefit of interferon in reducing relapses, disability progression, and MRI lesion activity and accrual. All of the available agents have been reported to reduce relapse rate, magnetic resonance imaging (MRI) lesion activity, and accumulation of disability in RRMS. Patients need to be seen on a regular basis after starting treatment to address potential side effects. This chapter discusses treatment of acute relapses, progressive multiple sclerosis and treatment in special populations including children.