Pentagalloylglucopyranose (PGG) is a natural product with widespread occurrence in the plant kingdom. It is present in various tissues of studied plants. PGG is synthesized in plants by covalently linking five galloyl groups to a glucose molecule through ester bonds. Two different linkages between the galloyl group and the anomeric center of the glucose core, carbon 1, are possible (Fig. 1). Both isomers were isolated from natural sources. However, it has been found that β-PGG is much more prevalent than α-PGG. Nevertheless, α-PGG has been identified in some plants . Because of its prevalence, most previous studies were performed with β- PGG, not α-PGG. Unless otherwise specified, the terms “PGG” and “β-PGG” are used interchangeably in this article. PGG was found in some medicinal herbs that were used as agents to treat stomach disorders and other diseases . Because of these interesting bioactivities and medicinal effects, PGG may be used as a model compound for the use of other polyphenolic compounds (tannins) in biomedical research and therapeutic development. This article reviews the progress of research on PGG, including its distribution, bioactivities and therapeutic potentials.