During childhood, adolescence, and young adulthood, the human brain undergoes both structural and functional development in order to support an expansion of behavioral repertoire and enhanced cognitive capabilities. During this period of plastic remodeling, there is also increased risk for psychiatric illnesses that often begin during this period. Increasingly, major mental illnesses are conceptualized as disorders of brain development. Understanding brain development is therefore a prerequisite for early detection and intervention for youth at risk. Our work seeks to both define normal pattens of brain development, and also delineate how abnormal brain development is associated with psychiatric symptoms such as mood disorders or psychosis. To do this, we use multi-modal neuroimaging within large-scale studies such as the Philadelphia Neurodevelopmental Cohort (PI: Raquel E. Gur). Ongoing work funded by the National Institute of Mental Health investigates how changes in brain development may confer vulnerability to symptoms of irritability across traditional categories of psychiatric diagnosis. Moving forward, we hope to use data-driven imaging methods in order to help tailor early interventions to youth at risk of disabling psychopathology.