Phosphoglycerate kinase (PGK) is an essential metabolic enzyme for all living organisms. It catalyses the high-energy phospho-transfer reaction from 1,3-bisphosphoglycerate to the beta-phosphate of ADP and thereby produces ATP. In mammals, PGK has more widespread roles, particularly in oncogenesis and in activating anti-retroviral drugs. Namely, PGK exhibits specific thiol-reductase activity important in the inhibition of plasmin-mediated angiogenesis required for solid tumour development. The phosphorylating activity of PGK, however, has been additionally proved to be involved in specific activation of antiviral and antitumour nucleotide-analogue drugs. In addition, the simple two-domain structure of PGK has served as a good folding-model of multidomain proteins. From folding-studies, not only the possible role of domains in the self-organisation process has been exemplified, but characteristics of the sophisticated protein misfolding mechanism has also been described. Besides the pathological anatomy (misfolding), the pathological physiology (misfunction) of PGK is also overviewed. Human phosphoglycerate kinase mutations have been identified to be associated with various serious diseases, such as mild to severe haemolytic anaemia, neurological disorders, mental retardation, behavioural aberrations, and neurological symptoms. These aspects are also discussed and summarised in this volume.