Because of such a complexity in cosmetic science, it was not possible to cover in a useful manner all the aspects in one book. Details in most of the above fields are covered in the different volumes of the “ Cosmetic Science and Technology” series. In the first edition of the “ Handbook of Cosmetic Sciences and Technologies,” we especially aimed at producing a useful formulation guide and a source of ideas for developing modern cosmetics. Four years later, with the second edition of the handbook, about 20 chapters were added, while the others were updated by trying to cover the most recent innovations in terms of ingredients and cosmetic vehicle forms that should orient the type of products of the future. The third edition is very different from the first two. A few chapters were updated from the first editions, but most are new, and the outstanding contributors were asked to deeply explain the science behind the products, ingredients, or methodology. Thus, the third edition may be seen, in some instances, as complementary to the two first editions.