The increased demand for nitrogen for world food production and the problems imposed by the decrease of fossil energy reserves stimulate research on biological nitrogen fixation. These practical demands on research can be answered by important successes of fundamental research. The introduction of the 15N2 methods and more recently the C2H2 method has made it possible to demonstrate N2 fixation in a rapid and reliable way. Since the enzyme system, nitrogenase, was obtained in a cell-free condition rapid progress has been made in elucidating the biochemistry of N2 fixation and the regulation of its activity. The successful application of the methods of microbial genetics has made it possible to locate the nif genes on the bacterial chromosome and to transfer these nif genes to originally non-N2 fixing bacteria. Stimulating experiments were performed on the regulation of enzyme synthesis and the role of the NH,-binding enzyme glutamin synthetase. Special attention was given to the protection against 02.