'One Health' as a discipline links human and veterinary medicine as co-equal partners in an increasingly efficient joint venture into health promotion and prioritised research. 'One Toxicology' is proposed as a way to reunify toxicology as a component of 'Ecosystem Health' and the encompassing 'One Health'. Ecotoxicology, which includes wild animal, plant and microbial communities, is a critical component of 'Ecosystem Health'. 'One Toxicology' is proposed to help hold toxicological sciences together and maintain intimate connections to medicine in general. 'One Toxicology' is efficient because biochemical systems are highly conserved and, thus, when one group of species is at risk, other groups of species are also often at risk. Fortunately, in the case of toxicological risk, problems can be avoided, because humans can minimise exposures. Historically, human health has benefited immensely from studies of the impacts of chemicals on laboratory animals and wildlife. Similarly, veterinarians and wildlife managers have learned from careless or accidental poisonings of humans to protect the health of both domestic and wild animals. Yet, newly discovered emerging toxicoses abound, and well-known toxicoses persist - to the detriment of all life forms, including our own. Thus, in the 'One Toxicology' of the future, disciplinary boundaries should more rapidly blur. If this is done well, physicians, various public health specialists, veterinarians of many disciplines, wildlife health specialists, ecologists and an array of toxicologists will share and rely upon disparate sources of information with increasing efficiency to facilitate diagnosis and management of poisoning; to prevent unwanted, unwise, and unnecessary toxic injury to human, animal, plant, and microbial components of biodiversity; to decrease nutrients available that enable toxigenic species; and to prevent releases of chemical contaminants that indirectly set the stage for infectious diseases.