MRI is the dominant neuroimaging modality for multiple sclerosis (MS). Revised diagnostic criteria formally incorporate abnormalities on MRI for diagnosis. MRI is well-suited for evaluating dynamic changes in MS patients. The suppression of new gadolinium-enhanced T1-weighted and newly active T2-weighted lesions on MRI are now standard outcome measures in clinical trials. This article reviews how conventional and advanced MRIs provide important biomarkers of MS pathology and considers the role of MRI outcomes in clinical trials and in clinical practice.