The early historical background of the discovery of poly(ADP-ribose) and the following development of science on poly(ADP-ribose) are reviewed. Fundamental knowledge on the natures of poly(ADP-ribose), poly(ADP-ribose) polymerase and enzymes degrading poly(ADP-ribose) are summarized with brief description on the methodology for their purification and characterization. Future prospect of research on biological significance of poly(ADP-ribose) has also been discussed briefly.