Claviceps purpurea is a fungal pathogen that infects rye and occasionally other grains. This dangerous plant disease is commonly known as ergot, and it produces toxic alkaloids that can cause hallucinations, convulsions, and even death in both humans and animals. Ergotism, the condition that arises when these alkaloids accumulate in the body, has been documented since the Middle Ages and has been associated with outbreaks of mass hysteria, religious fervor, and witchcraft. Other synonyms for Claviceps purpurea include ergot fungus, rye ergot, and fungal sclerotium. Early detection and eradication of the fungus are crucial to preventing the spread of the disease and protecting the health and safety of consumers.