Psychological distress is a set of painful mental and physical symptoms that are associated with normal fluctuations of mood. In some cases, however, psychological distress may indicate the beginning of major depressive disorder, anxiety disorder, schizophrenia, somatisation disorder, or a variety of other clinical conditions. In this book, the prevalence and correlates of psychological distress, including issues in relation to bullying victimisation, poly-victimisation, obesogenic behaviour, ideal cardiovascular health behaviour, and HIV status, were studied in 19 countries. The results will inform researchers and readers of the relevance of school and youth mental health programs and related policies targeting psychological well-being in the adolescent population.