This chapter describes the role of orthodontics as an adjunct to periodontal therapy. The primary objective of periodontal therapy is to restore and maintain the health and integrity of the attachment apparatus of teeth. In adults, the loss of teeth or periodontal support can result in pathologic tooth migration involving either a single tooth or a group of teeth. This may result in the development of a median diastema or general spacing of the teeth, rotation or tipping of premolars and molars with the collapse of the posterior occlusion and decreasing vertical dimension. Adjunctive orthodontic therapy is necessary to resolve these problems. This chapter covers the rationale for orthodontic treatment in periodontal therapy, use of orthodontics as an adjunct to overall treatment, indications and contraindications of orthodontic therapy, timing of orthodontic procedures in periodontal treatment, and iatrogenic effects associated with orthodontic treatment.