Preventive orthodontics is the action taken to preserve the integrity of what appears to be a normal occlusion at a specific time. Profit and Ackermann (1980) has defined it as prevention of potential interference with occlusal development. Preventive measures undertaken as part of preventive orthodontics include parent counselling, caries control, space maintenance, exfoliation of deciduous teeth, surgical correction of high renal attachments, treatment of locked permanent first molars, and prevention of oral habits. This chapter describes in detail space maintenance in deciduous and mixed dentition, the elimination of oral habits leading to interception and resolution of crowding by serial extraction.