The 4th International Conference on Substorms (ICS-4) was held at Lake Hamana, Japan on March 9-13, 1998. This volume represents a snapshot of substorm research as of 1998. The proceedings address the following key questions: what are the major expansion phase activities seen in various regions?; what triggers the substorm expansion onset?; what are the roles of waves and microscopic processes in large-scale substorm processes?; what is the relationship between global convection and substorms?; and what is the role of the inner magnetosphere during substorms? For each of the five key questions, the status of observational and modelling efforts in the field is presented in the invited and contributed papers. This volume will foster communication between magnetospheric and high-latitude ionospheric physicists and those scientists who are working primarily in the area of the thermosphere and low-latitude ionosphere.
