Periodontitis is the number one cause of tooth loss in the United States for adults thirty years and older. Periodontal disease affects over seventy-five to eighty percent of adults, and more recently has been found to have major implications for systemic health especially for patients with diabetes and high blood pressure. In 2017 the American Academy of Periodontology (AAP) and the European Federation of Periodontology (EFP) collaborated to create a new classification for periodontal disease and peri-implant diseases. The goal of this revised edition is to review this classification and contrast it to the 1999 classification as well as evaluate its impact on periodontal diagnosis, prognosis and therapy. Understanding Periodontitis not only reviews the categories of periodontitis, but also provides a detailed informative resource on diagnosing, categorizing and treating periodontitis. By utilizing illustrations as well as actual pictures of various procedures, it works well also as an interactive informative hand book that dentists, hygienists, as well as dental patients alike will benefit from to better understand periodontal disease.