Rapid progress in the field of organophosphate compounds has made this new edition necessary. Particular attention has been paid to new developments in biologically active products as this is probably of greatest interest to practical chemists. I have therefore updated the chapter on chemistry and, in connection with this, rewritten the chapter on metabolism. I should especially like to thank Professor Dr. HELLMUT HOFFMANN for his constant encouragement and interest in my work and for many fruitful discus sions. The co-author to the 1st edition, Dr. KARL-JULIUS SCHMIDT, died suddenly on November 21, 1980. I treasure the memory of a valued colleague of many years standing. Elberfeld, January 1982 CHRISTA FEST VII Preface to the First Edition Our intention has been to provide a short introduction to the chemistry and mode of action of insecticidal phosphoric acid compounds, with particular ref erence to the relationship between structure and activity. The yearly produc tion of these pesticides is now approaching 100,000 tons and thus offers an im portant example of applied research. If, however, one examines the historical development of these compounds, it is apparent that this was preceded by a hundred years of pure chemistry of phosphorus.