Root hairs increase the surface area of roots to the point that they can comprise a significant portion of the entire absorptive surface of root systems. Root hairs do this at rather minimal carbon cost, because of their range of sizes. A question posed by the author is whether, besides high rates of respiration, roots have any additional roles in the function of the rhizosphere. He presents hypotheses on this subject from a holistic point of view. The book covers the occurrence, life history, cytology, anatomy, morphology and physiology of root hairs. It also analyses the critical role of root hairs in the development of nodules - rhizobial and actinorrhizal in the process of symbiotic nitrogen fixation. Less well known, but still important, is the role of root hairs in mycorrhizal symbioses and their importance for the mineral nutrition of plants.