The original aim of this book was to cover different aspects of the tradi­ tionally "filamentous" potex-, carla-, poty-, clostero-, and capilloviruses. The title The Filamentous Plant Viruses seemed the only suitable one, but it has led us to discuss also the quite different filamentous viruses of the rice stripe group-recently officially named the tenuivirus group­ which otherwise, indeed, might not have been conveniently covered in any volume of this series. The question must be asked: What is there new that justifies the presentation of a book of this kind? An outline of the answer may be Among the traditional filamentous viruses, much pro­ given as follows. gress has been made in elucidating the physical structure of potexvirus particles, and this work serves as an excellent model for discussion of and future experiments on the poty-, carla-, clostero-, and capilloviruses, which have comparable structures, although they are more difficult to manipulate. Work on the structure and strategy of the genomes of poty­ viruses is, however, relatively advanced and at a very interesting stage. The helper component that assists the aphid transmission of potyviruses has also recently received considerable attention, although the more we know about that, the less seems clear about the aphid transmission of the carlaviruses and closteroviruses, which apparently neither possess nor require a helper component.