This article discusses the principles, products, and techniques currently available for local delivery of antimicrobials in the treatment of adult periodontitis. Four principles provide the scientific basis for the treatment of periodontitis: it is caused by bacteria; it cannot be cured, but it can be controlled; clinicians cannot remove all the plaque and calculus; and periodontitis reinfects. This article stresses how the local delivery of antimicrobials can help the clinician achieve the goals of arresting the disease and maintaining the disease in the arrested or controlled state. Rationales for reevaluating the treated patient and treatment options are presented. Local-delivery systems are reviewed, stressing those available in the United States. Pharmacokinetics, multicenter randomized trials, and techniques are presented.