Book excerpt: This model has been expanded across several levels of analysis, including cultural, macro-social, and cellular factors. The 2nd edition also features: Greater emphasis on translating research into practice and policy. Two new sections on risk and protective factors for disease and another on social and structural influences that affect health such as socioeconomic status, reflect the current scholarship in the field. More on prevention and/or interventions and treatment in the applications section. The book opens with the fields central theories including a "newer" stress theory that emphasizes the interaction of biological and social systems. Part 2 reviews the mechanisms that help us explain the link between health and behavior across diseases and populations. The all new Part 3 focuses on variables that lead to the onset and progression of major diseases or that are instrumental in promoting health.