The phenomenon of high complexity has multiplied in the adolescent population as a consequence of growing social, economic, technological or educational demands and pressures. “High complexity” in mental health is not a new phenomenon. It is present in patients who, due to their family and social situations, their early traumatic experiences or their emotional vulnerabilities, accumulate difficulties in various areas and present complex needs. This book studies and evaluates the characteristics and difficulties that these adolescents present, as well as their healthcare needs and those of their families. On the other hand, it presents various intervention designs to address especially complex cases and the resources available from the public health network to care for young people with mental health problems.