Coniferous trees are widely distributed in the world and have tremendous environmental and economic importance. Large numbers of bacteria live in the rhizosphere or rhizoplane of their roots, and some of these may promote tree growth through a variety of mechanisms. Known as plant growth-promoting rhizobacteria (PGPR), such bacteria can promote growth either directly, by liberating growth-regulating substances and increasing nutrient availability in the rhizosphere, or indirectly, by inhibiting plant pathogens, activating the systemic acquired resistance of plants, or stimulating the growth of other microorganisms beneficial to plant development. PGPR have great potential for use in plant nurseries, where they can help produce healthy and vigorous seedlings for commercial use, and in the restoration of degraded soils.