It is a tradition in orthodontics to divide patients grossly according to different Angle classes, as if all Class II cases, for example, would be similar. Therefore, it is not surprising that the well planned and conducted randomized controlled studies have come to a common conclusion: there is great individual variability in the craniofacial growth among untreated controls and also among treated individuals. Despite the importance of this conclusion, the issue has received only little attention. The present lecture is concerned about variability in the initial condition of the patients, differences in the growth and treatment timing and treatment response.