The overwhelming majority of patients with periodontitis are treated in the offices of general practitioners and the most common services rendered are non-surgical in nature. This Guide addresses the subject of non-surgical therapy from the perspective of evidence-based dentistry to include a discussion of the etiology of periodontitis and the need for therapy as the basis for a rationale for treatment. The assessment of non-surgical treatment outcomes with a view to decisions regarding further treatment is a prominent feature of the Guide. The discussion of non-surgical approaches goes beyond mechanical debridement to include subgingival irrigation, systemic antibiotics and locally delivered antibiotics. Treatment planning decisions and the maintenance phase of therapy are also discussed. This edition includes updates from research published over the past three years, providing valuable guidance to the clinician providing periodontal care.