The most rewarding aspect of writing a book is receiving encouraging comments from one's colleagues, since one always wonders whether fair coverage was made of the work of others or whether some omissions were made. I feel very fortunate that many colleagues took the time to read the first edition of this book and chose to use it as a textbook in their teaching. During the past few years they have given me valuable suggestions by pointing out areas that needed to be added to improve the book. Toxicology is one of the fastest moving scientific fields. In the areas of insecticide toxicology many new advances have been made since this treatise first appeared. Therefore, it would not be easy to write even a review paper that would not be outdated by the time it was published. In revising this volume I have made a conscious effort to adhere to the basic principles which have been developed over the years. While I have retained the basic framework of the original book, advances that fundamentally change certain concepts or add a new horizon have been chosen for updating those fields where applicable. The main emphasis has been placed on the addition of new sections and new compounds developed since 1975. Since the first edition appeared, several books covering technical details in each group have been published. They are excellent encyclopedic resources in their chosen areas, and are listed in each section as recommended reading material.