MRI techniques, including conventional T(2)-weighted and gadolinium (Gd)-enhanced T(1)-weighted images, have provided important insights into the pathophysiology of MS. Although the correlation of MRI measures with clinical disability and outcome continues to be investigated, MRI measures are routinely used both in clinical practice and in MS research. In addition to its use as a diagnostic tool, MRI is used as a surrogate marker to monitor disease progression and response to therapy. A variety of MRI measures are used in drug development studies and have aided our understanding of the potential benefits and possible mechanisms of action of drug therapies. Advances in MRI techniques may further elucidate the pathology of MS, thus providing opportunities for new treatment strategies.