There is a need to modify the definition of attached gingiva (AG) as it applies to healthy and diseased teeth and implants. There are two parts to this new definition: Part A is when the biologic width is supracrestal (epithelial attachment and gingival fibers) and is attached to a healthy tooth or tissue-level implant, and the zone of AG is measured from the base of the sulcus to the mucogingival junction (MGJ); Part B is when the biologic width is subcrestal—as with infrabony defects on periodontally involved teeth, periodontally involved tissue-level implants, and bone-level implants placed at or below the bone crest—and the zone of AG is measured from the bone crest (not the base of the sulcus) to the MGJ. Further, what the AG is actually attached to around teeth and different types of implants, and the clinical significance of these differences, are thoroughly discussed.