During the preschool age, children acquire a rapid increase in intellectual ability, social development, and complexity in language. Along with this revolutionary change, some children begin to confront with parents, experience jealousy and develop sense of guilt. Behavioural abnormalities manifest when children externalize these difficulties resulting aggression, delinquent behaviour, autism and temper tantrums and are at a greater risk of developing psychiatric disorder in later life. These disorders have a very good prognosis if treated at the onset. Therefore, these disorders must be identified early and referred to appropriate care. Because parents and health care workers do not have ability to identify behavioural problems at an early stage, most children are referred at an advanced stage of the disease. Therefore, a simple, sensitive and relatively inexpensive screening instrument that can be used routinely is essential to identify these problems in the community. This book focuses on developing and validating such screening instrument that could be used to screen behavioural problems of preschool children.