Growth and development is the net result of environmental modulation of genetic inheritance. Most craniofacial anomalies and dentofacial deformities result from inherited mutations and aberrant environmental modulation of multiple genes. The complexity of craniofacial growth and development can never be underestimated; it offers tremendous intellectual challenges to those who attempt to comprehend it. The controversies surrounding the use of dentofacial orthopedics to correct a developing maxillomandibular discrepancy-ie, growth modification-have been based to a large extent on evolving concepts concerning the biological mechanisms of craniofacial development and growth.Throughout its history, the field of orthodontics has been home to a number of competing but credible treatment approaches. Despite their obvious differences, virtually all these orthodontic approaches share at least one fundamental characteristic: their rationale is based on opinions regarding the biological mechanisms of the development and growth of the craniofacial skeleton and dentition, and on the etiology and natural history of malocclusion and dentofacial abnormalities.