The idea of Volums 4 and 5 of this series is a combination of a very condensed but broad review, handbook and textbook on most of the theoretical and practical aspects of pyrethroids of interest to chemists, biologists, pharmacologists, toxicologists and other people involved in insecticidal research, development, ecotoxicolo­ gy, application, patenting and commercialization of pyrethroids, as seen from a point of view of an industrial chemist once actively in volved in pyrethroid research. In order to provide a mode1 data base for testing quantitative structure activity relationships, the unique wealth of the numerous and diverse biological data dispersed in the literature is listed in about 110 tables, put in relation to each other and other standard compounds, together with many structural formulas of the com­ pounds involved. A number of data are published for the first time. Some of the more important reeent QSAR-studies are briefly acknowledged. Conformational aspects of bioactive pyrethroids are discussed (from synthesis, QSAR, X-ray); some of the X-ray derived conformations are published for the first time. The molecular basis of pyrethroid biological action is taken into consideration as intensively as possible. Stereochemical aspects are considered wherever they are involved in synthesis, biological activity, mode of action, metabolism (Vol. 4), and particularly in the complex problems in the production and relation of iso­ merically enriched trade products (Vol. 5). Since pyrethroid research is now, in manyaspeets, a finished chapter of applied research, a historieal treatment of the course of inventions is given (inventions, patent priorities).