Technical Abstract: Following a brief history of ergot alkaloids and ergotism, this review focuses on the metabolism and mechanisms of action of the ergot alkaloids under complex animal-plant/endophyte-environmental interactions to provide models of how these alkaloids afflict grazing livestock. A brief discussion the alkaloid chemistry is presented to orient the reader to the structure-function relationships that are known to exist for the alkaloids. Where appropriate, the medical literature is used to aid interpretation of livestock research and to provide insight into potential modes of action and alkaloid metabolism where it is not known for livestock. In closing the paper, we discuss management of ergot alkaloid intoxication in livestock and future research needs for this field of study.