The first, single-volume edition of this Work was published in 1955 and the second in 1970; continued demand prompted a third edition in two volumes which appeared in 1983. The first two editions were edited by myself alone, but in preparing the third, which was much longer and more complex, I had the crucial help of Peter Haasen as coeditor. The third
edition came out in 1983, and sold steadily, so that the publishers were motivated to propose the preparation of yet another version of the Work; we began the joint planning for this in
early 1992. We agreed on the changes and additions we wished to make: the responsibility for commissioning chapters was divided equally between us, but the many policy decisions, made during a series of facs-to-face discussions, were very much a joint enterprise. Peter
Haasen was able to commission all the chapters which he had agreed to handle, and this task (which involved detailed discussions with a number of authors) was completed in early 1993. Thereupon, in May 1993, my friend of many years was suddenly taken ill; the illness worsened rapidly, and in October of the same year he died, at the early age of 66. When he
was already suffering the ravages of his fatal illness, he yet found the resolve and energy to revise his own chapter and to send it to me for comments, and to modify it further in the light of those comments. He was also able to examine, edit and approve the revised chapter
on dislocations, which came in early. These were the very last professional tasks he performed. Peter Haasen was in every sense coeditor of this new edition, even though fate decreed that I had to complete the editing and approval of most of the chapters. I am proud to share the title-page with such an eminent physicist.