Natural toxins are commonly used to subdue or incapacitate potential prey organisms but may also act as a defence against predators or parasites. Additionally, these compounds may act to give their producers an advantage when competing for food and other natural resources. Competing organisms may also deploy their own counteractive chemical measures in a form of biological warfare.

Because of their enormous range of bioactive properties, many natural toxins have been isolated and refined for human use, where the difference between beneficial and detrimental effects is a matter of dose. These conflicting roles have played a critical role in the history of natural toxins including their refinement as pharmaceuticals, but also for their nefarious use as deliberate poisons. In many instances this history goes back several hundred or even thousands of years. Natural toxins have, therefore played a prominent part in human folklore (including some fiction). The history of these compounds and related folk tales, therefore, represent a major theme of the book.