Given that international and national agendas determine as priorities prevention and early intervention to mitigate the impact of mental health problems, it is critical to screen and identify groups at risk of mental and behavioural disorders, as well as promote mental health and socio-emotional well-being of individuals throughout life (e.g., children, adolescents, adults, elderly people, and other vulnerable groups). This Special Issue of Healthcare, entitled "Mental Health Promotion and Illness Prevention in Vulnerable Populations", welcomed original contributions of relevance to this area of research from different settings, cultural backgrounds, and academic disciplines in order to address groups at risk for mental disorders.