Nine years have elapsed since I wrote the first English edition of this book, and progress in hair science has made a second edition necessary. Since 1978, at least two new m~or scientific cosmetic journals have appeared, and four International Hair Science Symposia and one International Symposium on Forensic Hair Comparisons have been held. Thus, continuing studies in hair science have been numerous in the past nine years, so much so that a large proportion of the text had to be completely rewritten. In addition, a number of omissions that were kindly pointed out by reviewers have been included in this edition, as well as corrections sent to me by readers. I sincerely hope that this new edition fulfills the original purposes: to provide a reasonably up to date and complete account of the chemical and physical properties and behavior of human hair, and to serve as a convenient starting point for hair research-and, as indicated in the first edition, not to be the final word.