Nowadays, an alarming number of juveniles all over the world find themselves implicated in the juvenile justice system and a great number of them are incarcerated in detention centres or even in jails for adults. The mean age of these youth has lowered dangerously, the percentage of delinquent females has increased dramatically, and the number of minority juveniles within this population has become unjustifiably high. The majority of these young people has diagnosable mental disorders, including substance abuse, learning disorders, ADHD, conduct disorder, anxiety and mood disorders, at rates much higher than in general same-age population. Very often, multiple diagnoses are applicable. Over the last years, experts from medicine, psychology, law, and sociology have been engaged in a number of evidence-based research studies, in order to study the relationship between juvenile delinquency and psychopathology. This research interest has resulted in a proliferation of studies mainly conducted at the U.S., with European countries following this activity. The objective of this book is to provide a comprehensive description of what is currently known in this area, with an emphasis on knowledge informed by empirical research. This way, it is aimed at providing a basis for the elaboration of an integrative perspective of psychopathology in juvenile delinquents and for the elucidation of the complex relationship between mental health disorders and juvenile delinquency. A developmental psychopathology approach is used as this is the area of expertise of the authors, especially regarding assessment, diagnosis and treatment of disruptive behaviour disorders.