Mental disorders are one of the greatest public health concerns of our time, and they are affected by social factors. To reduce the considerable burden of mental disorders, more global and systematic knowledge of the social determinants of mental health is necessary. This paper presents the results of the 27 studies included in the International Journal of Environmental Research and Public Health Special Issue, “Social Determinants of Mental Health”. The studies are grouped into four broad categories: social inclusion and mental health, young people’s mental health, mental health at work, and mental health service users. The results cover different countries, age populations, settings, and methodologies. Finally, the main findings on the relationship between social determinants and mental health are presented and summarized.