During the last decade it has become clear that bacteria-plant interactions play an important role in agricultural science. In particular, symbiotic nitro­ gen fixation, plant tumorigenesis, and plant pathogenic bacteria have been extenSively investigated. Therefore, several of my colleagues suggested the importance of organizing a specialized symposium on the "Molecular genetics of the bacteria-plant interaction". This symposium was held in Germany, at the University of Bielefeld, in the autumn of 1982. The International Program Advisory Board, together with the National Organizing Committee, initially decided to concentrate on the following three topics: 1. Rhizobium-plant interaction 2. Agrobacterium-plant interaction 3. Plant pathogenic bacteria In retrospect, these topics proved to be most popular: Nearly all important groups working in this field contributed to the Bielefeld Symposium. The papers presented are now published as the Proceedings. It will be obvious that this book represents the most comprehensive collection of papers describing the molecular genetics of the bacteria-plant interaction. Scientists, as well as students, can use this book to learn about the basic principles and the current ideas that have recently been developed in this growing research area. The Symposium was financed by the Bundesministerium ftir Forschung und Technologie (Federal Ministry of Science and Technology). I express on behalf of the Organizing committee its sincere appreciation to this sponsor, without whom the Symposium would not have been possible. In addition, the help of several industrial companies is acknowledged.