Vulnerability, the susceptibility to harm, results from an interaction between the resources available to individuals and communities and the life challenges they face. Vulnerability results from developmental problems, personal incapacities, disadvantaged social status, inadequacy of interpersonal networks and supports, degraded neighborhoods and environments, and the complex interactions of these factors over the life course. The priority given to varying vulnerabilities, or their neglect, reflects social values. Vulnerability may arise from individual, community, or larger population challenges and requires different types of policy interventions--from social and economic development of neighborhoods and communities, and educational and income policies, to individual medical interventions.