This group of materials tends to be relatively neglected, with regard to defect and diffusion studies, when compared with the other major semiconductor groups such as the elementals (Si, Ge) and the III-V compounds (especially GaAs). This is reflected by the fact that the volume of diffusion data is smaller than that for the other groups (see DDF volumes 153-155 on Si and volumes 157-159 on GaAs). Nevertheless MCT (HgCdTe), here classified as part of the (Cd,Hg)Te system, continues to be of great interest and this is reflected by the contents of this volume. In particular, the first of the original works in this book reviews the topic of diffusion in MCT.