Whilst the actual reduction of nitrogen gas (dinitrogen) to ammonia would appear to be a well defined process, many research questions concerning nitrogen fixation remain and continue to be addressed by diverse groups of scientists. This book presents the proceedings of the 13th International Congress on Nitrogen Fixation, held in Hamilton, Ontario, Canada, in July 2001. With very broad participation and a wide range of topics, it covers the most recent findings. In fifteen sections the main topics discussed include; bacterial genomics, plant genomics, development biology, signals in the soil, nodule metabolism and applied aspects of nitrogen fixation.