Various biological, psychological, and social-psychological models are used to understand adolescent suicidal behavior. Even with the range of theoretical approaches, mental health professionals are challenged to integrate this information into practice and policy. Biological theories propose that adolescent suicide emerges from biochemical components of psychiatric disorders, the biological transmission of suicidal risk across generations, maternal illness during pregnancy, a difficult birth process, or physical illnesses of adolescents. Psychological theories suggest that suicidal adolescents present external reasons for suicide attempts when the internal reason is to deal with rejection and deprivation. A key sociological theory is Durkheim's view that rates of suicide are based on the degree of integration into social institutions and regulation within society. Human ecological theory provides a multidisciplinary approach to understanding adolescent suicide that incorporates individual, environmental, and social system factors. Expanding the focus of prevention and intervention to encompass multiple levels of the human ecosystem provides greater opportunities to reduce suicidal behavior risk. The human ecological approach to suicidal adolescents integrates previous research and theory into multiple ecosystemic levels (organism, microsystem, mesosystem, exosystem, and macrosystem). In addition, the approach can be used to identify risk factors related to adolescent suicide, as well as prevention and intervention methods at each ecosystem level. The human ecological model has considerable potential for providing a framework for practitioners and in developing public policy.