No organism exists in isolation. Symbiosis describes some of the most intimate interactions that occur between organisms; those in which some species can overcome their own physiological limitations by exploiting the capacities of others. Symbiotic Interactions is a modern synthesis of our knowledge of symbiosis, from the molecular mechanisms underlying the establishment and function of symbioses to the ecological and evolutionary impact of such associations. The book takes the novel approach that symbiosis is a vehicle by which many organisms have gained access to complex metabolic capabilities, and this is illustrated by a variety of associations, including photosynthetic algae in corals, nitrogen-fixing bacteria in plant roots and cellulose-degrading microorganisms in herbivorous mammals. The traditional view of symbioses as mutually-beneficial associations is explicitly abandoned. This book brings together the scattered literature on symbiosis, providing an integrated introduction for undergraduate courses and up-to-date review for postgraduate students.