The thioredoxin redox system, consisting of the thioredoxin protein, thioredoxin reductase and NADPH, is found in both prokaryotic and eukaryotic cells. This essential redox system is known to be important in a multitude of biological functions, including cell cycle regulation and maintainuig an intracellular reduced state. The crystallisation of thioredoxin and thioredoxin-complex structures, covered in this study, has allowed for a detailed analysis of the active site region for the application of drug targeting. understanding of the specific requirements that thioredoxin has for its target substrates, and has thus allowed for pseudo structure based drug design.