This text provides a short review of venoms used by animals to defend themselves or to capture prey. Venomous or poisonous animals are widely distributed throughout the animal kingdom, with birds appearing to be the only large and widespread group in which no venomous species has been discovered. By research in this field scientists have learned, and will learn, much about animal behaviour and physiology. The active venom components, the toxins, have proved to useful tools for studying human physiological mechanisms. Because of the high specificity of certain toxins, it has been possible to resolve important links in complex physiological mechanisms with these substances.