Selection of patients for orthodontic treatment should be based on a thorough analysis of the consequences of malocclusions for the individual. The mere presence of deviations from the concept of the ideal occlusion should have no influence on orthodontic treatment decisions. According to available studies, the influence of malocclusion on periodontal health, speech and chewing is fairly minor. Neither can orthodontic treatment be justified as an effective means of preventing TMD but it may be indicated to reduce existing signs and symptoms of TMD in certain carefully selected cases. Interceptive or preventive orthodontic treatment may be indicated to reduce the negative influence on growth and occlusal development of functional malocclusions (anterior or lateral forced bite) or ectopic tooth eruption. Similarly, early correction of large overjet may be valuable in order to reduce the risk of traumatic injuries. Such treatment is usually motivated during the primary or mixed dentition periods. From the teenage period and onwards, psychosocial or aesthetic reasons for orthodontic treatment are dominating. Decisions to start orthodontic treatment in order to improve aesthetics should usually not be taken before the child has reached sufficient maturity for these decisions, normally after the age of 12 years. Special consideration needs to be given to subjects with craniofacial syndromes or handicap in order to develop effective treatment methods to promote as normal growth and occlusal development as possible.