Mycorrhizae have been a subject of scientific interest since the late 1800s. Much of the early interest and practical application concerned mycorrhizae's role in forest production. Recently, knowledge of fungi in the rhizosphere of agricultural plants has developed at a rapid pace. The authors of this volume have shown the importance of mycorrhizae, not only to plants but to the soil itself or, in other words, to the soil-plant system and its sustainability. Civilization itself depends on the sustainability of agriculture, and these microscopic organisms living in close association with plant roots play an important role in determining the sustainability of production methods that we impose on the system.