Alkaloids are levorotatory, basic, naturally occurring, heterocyclic, organic nitrogen containing compounds which are biosynthesized from amino acids by plants, microorganisms, and some animals. Many of them are pharmacologically active and are consequently used as drugs. The main precursors for alkaloid biosynthesis are ornithine, lysine, aspartic acid, phenylalanine, tyrosine, and tryptophan. For example, the alkaloid in tobacco, nicotine, is derived from ornithine, while phenylalanine and tyrosine give rise to simple alkaloids such as ephedrine or more complex ones such as morphine. Their chemical classification is based on the carbon-nitrogen skeletons. Ergot alkaloids, the subject of this chapter, are of the indole type and are derived from tryptophan. The ergot alkaloids are so called because they were originally derived from ergot, a sclerotium (twisted mat of fungal hyphae) formed as a disease on the grain of rye. The cause of the rye disease is a fungus, namely the ascomycete Claviceps purpurea. Ergot contains several highly potent alkaloids and the unwitting consumption of grain attacked by fungi producing ergot alkaloid has led to ‘ergotism’, a disease characterized by convulsions among other symptoms. This chapter presents nature of ergot alkaloids, uses of ergot alkaloids and their derivatives, production of ergot alkaloids, and the physiology of alkaloid production.