In an information society, heavily dependent on communications and distributed systems, feature interactions are likely to become an even more important problem than they are today. A particularly interesting issue, given the current work on agents, is whether feature interactions will be more likely in systems with many autonomous agents performing tasks. The current demand for better and more convenient communications requires development of a variety of new services as quickly as possible. As the number of services becomes larger, however, feature interactions create incompatibilities between the various functions needed to implement them. In developing telecommunication systems, we now spend huge numbers of person-hours on software modifications and testing whenever a new function is added. Much of this time is spent on detecting and eliminating problems arising from feature interaction. In the future, as ever more services are offered, feature interactions will become a major bottleneck in the development of software for telecommunications systems. This book presents opinions on the technical problems involved in feature interactions and definitions of features and feature interactions.