Thanks to the recent advances in mapping brain activation during task performance using functional Magnetic Resonance Imaging (i.e., studying the brain in action), it is now possible to study one of the oldest questions in psychology: how the development of neural circuitry underlies the development of cognition and emotion. The ‘Storm and Stress’ of adolescence, a period during which adolescents develop cognitively with great speed but are also risk-takers and sensitive to opinions of their peer group, has puzzled scientists for centuries. New technologies of brain mapping have the potential to shed new light on the mystery of adolescence. The approach proposed here concerns the investigation of brain regions which underlie developmental changes in cognitive, emotional and social-emotional functions over the course of child and adolescent development.For this purpose I will measure functional brain development longitudinally across the age range 8-20 years by using a combined cross-sectional longitudinal design including 240 participants. Participants will take part in two testing sessions over a four-year-period in order to track the within-subject time courses of functional brain development for cognitive, emotional and social-emotional functions and to understand how these functions develop relative to each other in the same individuals, using multilevel models for change. The cross-sectional longitudinal assessment of cognitive, emotional and social-emotional functional brain development in relation to brain structure and hormone levels is unique in the international field and has the potential to provide new explanations for old questions. The application of brain mapping combined with multilevel models for change is original, and allows for the examination of developmental trajectories rather than age comparisons. An integrative mapping (i.e., combined with task performance and with biological markers) of functional brain development is important not only for theory development, but also for understanding how children learn new tasks and participate in a complex social world, and eventually to tailor educational programs to the needs of children.