The area of virtual organizations, and industrial virtual enterprises in particular, is attracting a large and growing interest both in terms of the research and development and the implementation of new business practices. An ever-increasing number of international projects and national initiatives have been launched recently. Most of the earlier efforts are focused on the development of supporting infrastructures, although more and more initiatives now pursue the exploitation of this concept in business terms. Being a recent research and development area, and in spite of the mentioned interest, there is a lack of a structured and comprehensive text that can be used as a reference source. Most available literature is dispersed in several conference proceedings, journals, and book chapters. This book represents an attempt towards such structured text. Although the book was prepared in the framework of PRO-VE'99, a working conference on infrastructures for virtual enterprises organized by the Esprit project PRODNET II and IFIP, it has the goal of covering more generic VE requirements and addressing several other approaches and important aspects in this paradigm.