Over the years, dentists have had difficulty in correctly relating margin placement to the periodontal apparatus. Especially in the prosthetic treatment of the demanding, advanced, periodontal-prosthetic case, many failures (of periodontal health or or esthetics), have been due to the incorrect prosthetic management of the periodontal soft and hard tissues. These failures frequently have been blamed on poor oral hygiene and poor cooperation by the patient, but this is not always true. This paper, through the presentation of a literature review and clinical examples, discusses the important, correct relationship of the biologic width to the placement of the restorative margin. This relationship is vital to the achievement of long-lasting periodontal health.