This monograph is dedicated to one of the discoverers of poly(ADP ribose), Professor Paul Mandel, from the Centre de Neurochimie in Strasbourg. We would like to congratulate him for his distinguished contributions to the field of poly(ADP-ribosyl)ation and express our gratitude for his support in the last years and particularly for his encouragement for the organization of this meeting. Poly(ADP-ribose) was discovered more than 25 years ago. Since then, excellent progress has been made on the study of the mechanisms of poly(ADP ribose) reaction. The last five years have been particularly exciting since the development of various molecular biology techniques has revealed the complex nature of this multifunctional enzyme. Looking at the contributions presented at this meeting, it becomes obvious that more work at the molecular level is needed. Most likely, these experiments will shed some light on the functions of poly(ADP-ribose), but further ~iophysical studies will still be required to fully understand this complex enzymatic system.