Nitrogen fixation research uses the methods of and accumulating data from fundamental branches of biology and chemistry. These include: catalytic mechanisms; protein structure and function; molecular organization of genes and the regulation of their activities; biochemistry of plants and micro-organisms; the signalling and surface interactions between organisms; microbial taxonomy and evolution; formal and population genetics; and ecology. The relationships between biological nitrogen fixation research and different branches of applied biology are addressed and analyzed, such as: the monitoring of genetically engineered micro-organisms, selection of plant-associated microbes, plant breeding, increasing the protein content of crops, providing ecologically safe food production, and diminishing the chemical pollution of the environment.