This is the second issue, following DDF164, to cover recent progress in this field. The contents are contiguous with those of DDF164, and extend to late November or December 1999 (depending upon journal publication dates). As usual, priority in abstracting has been given to the most accessible work and, in particular, to those papers which furnish original data or report important new techniques, phenomena or anomalies, although there is also extensive coverage of more qualitative features of diffusion and defect phenomena, and of the predictions of computer models.