This book is a contribution of Dr Harald Loe (D.D.S, Dr Odont) in the field of Periodontology as well as in Dentistry. His constant zeal towards research and his desire to take the field of Periodontology to new heights, made him an eminent contributor as well as a great scientific mind. His contributions were not only limited to new scientific discoveries, but he also played an important role as a renowned clinician and a great mentor. It was because of his research that the role of micro-organisms as well as plaque was associated as a causative factor for the gingival and periodontal conditions. Thus this book is a tribute to one such great scientist of all times who opened new horizons for dentistry especially Periodontology.