Magnetization transfer (MT) imaging is a technique that enables measurements to be extended beyond those in conventional MR imaging sequences. Since its introduction, MT imaging has become a popular tool, partly because of its potential to change tissue contrasts, and partly because of its capacity to characterize tissues in a quantitative manner. MT imaging also has become particularly popular in the field of multiple sclerosis. Using this technique, a wealth of information has been generated on the natural history of the disease. This article explains the physical basis of MT imaging, describes applications of the technique in MS patients, and discusses the limitations of the technique in terms of standardization.