Recently, carbohydrates have come to the fore because of their central role in many biological processes. One area of current interest concerns the enzymatic modification of sugar nucleotides, in relation to both secondary metabolite glycosylation and the formation of complex cell surface-associated glycoconjugates. Bacteria, in particular, have proven to be a rich field in which to study these transformations, because they are often unique to specific classes of organisms. This has led to the realization that such microbial biosynthetic pathways might be exploited in the generation of novel antibiotics, or indeed serve as targets for such compounds. This work illustrates the interplay between protein structure determination, chemistry, and molecular biology in providing insight into the mechanism of such biochemical transformations.