This paper was prepared by the Research, Science and Therapy Committee of The American Academy of Periodontology and is intended for the information of the dental profession. The purpose of the paper is to provide the reader with a general overview of the relationship of tobacco use and periodontal diseases. This paper will review the epidemiological and clinical findings that have led to our understanding of the role of tobacco use in relation to periodontal diseases and their treatment. In addition, this paper will review the possible underlying mechanisms for these effects from tobacco use. The practitioner can use this information in treatment decisions and in giving advice to the patients who use tobacco products.