The book "Molecular Microbial Ecology of the Soil" offers a comprehensive analysis of molecular biological methods for studying rhizobial ecology, which is crucial for biological nitrogen fixation. It brings together contributions from experts in various disciplines, including molecular biology, microbiology, plant breeding, and soil science. The research findings stem from a coordinated research program by the FAO/IAEA conducted from 1992 to 1996. The aim was to develop innovative methods to better understand the interactions between legumes and rhizobium bacteria. These insights are particularly relevant for improving legume yields in regions such as Africa, Asia, and Latin America, where they serve as an important source of protein. The book is aimed at scientists working on biological nitrogen fixation, microbial soil ecology, and legume production.