Isoprenoids constitute one of the most diverse classes of natural products. As a compound class, they are essential to basic metabolic processes including cell-wall biosynthesis, post-translational protein modifications, and signaling. In addition, isoprenoid secondary metabolites are highly valuable natural products with a wide range of biotechnological applications. The biosynthesis of their two universal building blocks, isopentenyl diphosphate and dimethylallyl diphosphate, was thought to proceed exclusively by way of mevalonate as a key intermediate until a novel pathway involving methylerithritol phosphate (MEP) was discovered in the early 1990s. In this review, we describe the seven enzymes of the MEP pathway, along with their discoveries, three-dimensional structures, and mechanisms. The latter include examples of remarkable enzyme catalysis including an unusual cytidilation reaction and the use of iron-sulfur cluster cofactors in reductive ring opening and hydroxy-group elimination. Furthermore, isoprenoid biosynthesis shows a characteristic species distribution. A brief overview highlights the MEP pathway's potential as a selective drug target, which is absent in humans but essential to the survival of many important bacterial and apicomplexan pathogens.