This work is intended for a range of readers, including scientists, students and informed laypersons who are interested in agricultural biotechnology, alternative agriculture, bioremediation of the environment and decreasing our reliance on pesticides and fungicides. It deals primarily with understanding, at a biochemical and molecular level, how certain free living bacteria are able to promote plant growth; symbiotic bacteria such as Rhizobia are mentioned only briefly. The assumption underlying the endeavour is that a more profound understanding of these fundamental mechanisms will eventually permit scientists to manipulate these bacteria and use them more efficiently as a regular component of agricultural and/or horticultural practice. Therefore, while all the topics are discussed in as comprehensive a manner as possible, the book emphasizes a critical overview of the field rather than a mere compendium of data.