The soil-transmitted nematode parasites, or geohelminths, are so called because they have a direct life cycle, which involves no intermediate hosts or vectors, and are transmitted by faecal contamination of soil, foodstuffs and water supplies. They all inhabit the intestine in their adult stages but most species also have tissue-migratory juvenile stages, so the disease manifestations they cause can therefore be both local and systemic. The geohelminths together present an enormous infection burden on humanity. Those which cause the most disease in humans are divided into three main groupings, Ascaris lumbricoides (the large roundworm), Trichuris trichiura (whipworm), and the blood-feeding hookworms (Ancylostoma duodenale and Necator americanus ). The Geohelminths: Ascaris, Trichuris And Hookworm, Volume two of `World Class Parasites', is written for researchers, students and scholars who enjoy reading research that has a major impact on human health, or agricultural productivity, and against which we have no satisfactory defense. It is intended to supplement more formal texts that cover taxonomy, life cycles, morphology, vector distribution, symptoms and treatment. It integrates vector, pathogen and host biology and celebrate the diversity of approach that comprises modern parasitological research.