Adolescence and young adulthood are critical life stages for the mental health of the individual, as they are characterized by significant changes at the physical, social, emotional, and cognitive levels. The degree to which psychological developmental tasks are mastered during these phases of life has a decisive influence on later life, as does the complicated interplay of condition factors and systemic influences. We are particularly interested in factors which, under the aspects of equifinality and multifinality, can contribute to the explanation and prediction of differential development paths. A focus here is on the investigation of objective and subjective socio-economic status, mental health literacy, and aspects of self-efficacy in well-being, quality of life, and the development of psychological symptoms in adolescence and early adulthood. A further focus is the investigation of the use of care services and the associated perceived barriers from the point of view of adolescents.