This chapter concerns emotional, behavioural and developmental disorders that arise in the first two decades of life. Few formal tests or assessments can contribute to the clinical assessment for common behavioural and emotional disorders. Clinical physiological assessments can provide helpful information for neuropsychiatric disorders. Risks for psychopathology occur from a variety of sources both internal and external to the child. Many children and adolescents demonstrate an ability to withstand exposure to risk processes and not develop psychiatric disorders. Disturbances in parent-child relationships in infancy significantly influence the development of psychopathology. Hyperactivity and impulsivity are more closely associated with each other than either is to attentional difficulties. Autistic syndromes are lifelong disorders even in those who show real improvements by young adult life. Child psychiatrists should continue to contribute to basic research aimed at understanding the causes of mental illness and behavioural syndromes.