The only known approach to prevention of periodontitis is to prevent gingivitis, which from several points of view has been seen as a worthwhile endeavour. The principles to prevention include the regular and consistent removal of plaque, supragingival and subgingival, soft and mineralized, i.e. calculus from the teeth and gingival crevices. This chapter deals with the methods of oral hygiene assessment and stages of periodontal disease progression, an understanding of which forms the basis for prevention. There are three essential approaches to prevent periodontal disease. These are mechanical plaque removal by individual, mechanical plaque removal by dental professional and chemotherapeutic method of plaque control. All these approaches and supportive periodontal therapy are explained in detail.