 Rhizobial biological nitrogen fixation is a symbiotic process that has been studied for centuries. It is driven by the presence of leguminous plants, which induce the formation of root nodules containing rhizobia. These nodules are able to convert atmospheric nitrogen into ammonium, which can then be used by the host plant. This process is essential for sustainable agriculture and has been intensively investigated from agronomic, plant physiological, microbiological and molecular perspectives. Despite significant progress, there remain several challenges related to the efficiency of nitrogen fixation in rhizobia. Research has focused on identifying key bottlenecks, such as the regulation of gene expression and metabolism, and the role of signalling pathways. This article was authored by Christina Lindstrom and Saeed Abdullah Musavi.