In the preface of the book Combinatorial Matrix Theory (CMT) I discussed my plan to write a second volume entitled Combinatorial Matrix Classes. Here 15 years later (including 6, to my mind, wonderful years as Department of Mathematics Chair at UW-Madison), and to my great relief, is the finished product. What I proposed as topics to be covered in a second volume were, in retrospect, much too ambitious. Indeed, after some distance from the first volume, it now seems like a plan for a book series rather than for a second volume. I decided to concentrate on topics that I was most familiar with and that have been a source of much research inspiration for me. Having made this decision, there was more than enough basic material to be covered. Most of the material in the book has never appeared in book form, and as a result, I hope that it will be useful to both current researchers and aspirant researchers in the field. I have tried to be as complete as possible with those matrix classes that I have treated, and thus I also hope that the book will be a useful reference book.

I started the serious writing of this book in the summer of 2000 and continued, while on sabbatical, through the following semester. I made good progress during those six months. Thereafter, with my many teaching, research, editorial, and other professional and university responsibilities, I managed to work on the book only sporadically.