This paper provides a synthesis of the literature on mental health and emotional well-being of children and adolescents, including an overview on the latest PISA 2015 results where relevant. The paper begins by providing a definition of the terms and a synopsis of mental health and emotional well-being trends among youths in the recent decades, including psychiatric disorders, life satisfaction, and bullying. Different factors underlie recent emotional well-being trends, such as sleep deprivation, increasing levels of stress and pressure and social relations. The contexts and environment that children live in today have been rapidly changing and can have a considerable impact on their well-being. Among effective prevention and intervention programmes for children and adolescents' depression, anxiety, and suicide, the most common element found is cognitive-behavioural therapy. This approach aims to improve children's problem solving, coping skills and to overcome negative thoughts and emotions. Efforts to collect more information on mental health indicators and information on relevant factors would be helpful for future research.