Book excerpt: This volume is written with the objective of covering the basic issues in biological nitrogen fixation such as: the physiology, biochemistry and molecular genetics of nitrogen fixation; and the role of signal molecules and host gene expression in nodulation and nitrogen fixation. The book also details recent developments in biofertilizer technology, such as: the immobilization of cyanobacteria; endophytic nitrogen fixation; and solubilization and mobilization of nutrients by phosphobacteria and VA mycorrhiza and their role as bioinoculants.