In every scientific discipline there are milestones - periods of significant accom plishment when it is appropriate to pause and summarize the state of the field. Such is the case for the study of the behavior of cosmic rays in the heliosphere. We are just passing through solar minimum conditions, when the heliosphere has a well-ordered and relatively simple configuration. We have been fortunate to have an array of spacecraft - unprecedented in the history of space exploration and unlikely to be repeated for generations - to provide comprehensive measurements of cosmic rays throughout the heliosphere. Ulysses has completed its historic first exploration of the heliosphere at high heliographic latitudes. Pioneer and Voyager have been exploring the outer heliosphere. The durable IMP-8 and now the WIND spacecraft have provided detailed baseline measurements at Earth. Concurrently, there has been a steady improvement in theoretical understanding of cosmic ray behavior through the use of ever more sophisticated numerical models. This milestone in cosmic ray studies was celebrated with a Workshop on Cos mic Rays in the Heliosphere which was convened by L. A. Fisk, J. R. Jokipii."

This volume gives a comprehensive and integrated overview of current knowledge about cosmic rays in the heliosphere. It is the result of a workshop at ISSI, where experimental space physicists as well as theorists presented and discussed their views on the behaviour of cosmic rays during the currently prevalent solar minimum conditions, when the heliosphere has a well-ordered and relatively simple configuration. An unprecedented array of spacecraft - Ulysses, Pioneer, Voyager, IMP-8, Wind, to name a few - in conjunction with ever more sophisticated numerical models made this possible, gave us our first clear view of the three-dimensional heliosphere at solar minimum, and have significantly advanced our knowledge. The status of the field is first presented in a series of introductory papers; these are followed by four Working Group reports attempting to synthesise this knowledge, make progress in our understanding, and point out directions of future research. A summary of the parameters used in cosmic ray modulation and an epilogue on conditions and consequences expected at the upcoming solar maximum conclude the volume. The book is intended to provide active researchers in space physics with an up-to-date status report and also to introduce the advanced graduate student to the field.