We have entered an exciting period in the study of multiple sclerosis and its treatment. Central to this progress has been the introduction of magnetic reso nance techniques. When Young and his colleagues published the first images of the brain in multiple sclerosis at the end of 1981, it was at once obvious that magnetic resonance imaging would playa major role in diagnosis. Intuitively one felt that it would also have a role in increasing our understanding of the pathogenesis of the disease and in monitoring treatment. And so it has proved. Important problems however remain, perhaps the most important of which at present is the weak predictive power of standard magnetic resonance ima ging methods in determining the possibility of progression of impairment and disability. Recently, there have been advances which promise to overcome some of these problems, but decisions about what approach to adopt in selecting patients for clinical trials and which techniques to use in monitoring treatment during their course are still difficult. In this book, Dr. Filippi and his colleagues have assembled an outstanding group of contributors whose work is central to the progress that is being made. The coverage of the issues involved in the use of magnetic resonance techniques in assessing therapeutic effect is comprehensive and, though the field is chan ging rapidly, the principles and much of the detail in the book are likely to have lasting value.