The structural analysis of all enzymes in a metabolic pathway is a prerequisite to answering fascinating questions, such as those relating to the evolutionary relationships between enzymes within the same and related pathways. Furthermore, the observed impressive diversity of catalytic functions displayed by these enzymes can lead to the synthesis of highly complex or unstable molecules, frequently involving unusual chemical reactions. Moreover, a detailed description of the active site of each enzyme in a pathway is of immense importance for the rational design of new drugs. The recent progress made in the structural biology of enzymes involved in NAD and molybdenum cofactor biosynthesis presents a significant step toward these goals.