As periodontal researchers and clinicians, we are challenged every day to make decisions relating to the clinical management of our patients and about how best to conduct clinical periodontal research. This volume of Periodontology 2000 addresses some of the critical issues in contemporary clinical periodontics and periodontal research that are of direct relevance to clinicians, researchers, teachers and students. The 11 review articles in this volume of Periodontology 2000 focus on aspects of periodontal research methodology and clinical periodontology. In terms of research methodology, the articles aim to inform the reader on topics relating to randomized controlled trials in periodontal research, evidence-based dentistry, calibration of clinical examiners and statistics relevant to periodontal research. The clinical periodontology articles address issues relating to decisions on retaining periodontally compromised teeth or replacing them with implants, periodontal management in the patient with osteoporosis, surgical approaches for root coverage and the emerging science of advanced regenerative technologies, including the use of stem cells, for periodontal regeneration. It is hoped that these critical reviews will address many of the dilemmas that confront us on a regular basis and provide practical guidance to those engaged in both clinical periodontology and clinical periodontal research.