Rhizobium species involved in root nodule formation on legume plants are one of the best known groups of micro­ organisms. The Rhizobium legume symbiosis continues to be of strategic importance particularly in the context of food production. As the world population grows, it is also neces­ sary to have new developments taking place in crop improve­ ment. The development and application of new technologies in biological sciences over the past number of years have made the entire area of plant-microbial interaction an exciting and challenging research area to be involved in. In view of the importance of symbiotic nitrogen fixation, it is not surpris­ ing that it still represents one of the priority areas for commercial development in agricultural biotechnology. Since this symbiosis involves an association between procaryotic and eucaryotic partners, it requires of necessity a co-ordinated and interdisciplinary approach. It was in this spirit that this international conference was organised. The scientific programme was designed to focus on physio­ logical limitations affecting symbiotic nitrogen fixation and the potential for overcoming such limitations using genetic technologies. Participants were drawn from contractants of the EEC DGVI "Energy in Agriculture" nitrogen fixation prog­ ramme. The scientific programme was also supplemented with invited scientists from Europe and North America to provide appropriate expertise on the various conference topics.