"Collective violence" is defined as "the instrumental use of violence by people who identify themselves as members of a group--whether this group is transitory or has a more permanent identity--against another group or set of individuals, in order to achieve political, economic, or social objectives." Forms of collective violence include wars, terrorism, and other violent political conflicts; state-perpetrated violence such as genocide, repression, and other abuses of human rights; and organized violent crimes such as banditry and gang warfare. The World Health Organization estimated that approximately 310,000 people died from war-related injuries in 2000. The risk factors for violent conflict include political factors (lack of democratic processes and unequal access to power); economic factors (grossly unequal distribution of resources, unequal access to resources, control over key natural resources, and control over drug production or trading); societal and community factors (inequality between groups, the fueling of group fanaticism, and the availability of small arms and other weapons); and demographic factors (rapid demographic change). The consequences of collective violence impact infant mortality, communicable diseases, disability, and mental health in the health sphere, as well as specific populations such as civilians and refugees and internally displaced people. There will also be demographic and socioeconomic impacts. The prevention of collective violence involves a reduction in the potential for violent conflict, the promotion of compliance with international agreements, the potential benefits of globalization, and health care services. Public health responses to violent conflicts should encompass service provision during conflicts, ethical considerations of aid provision, community involvement, and the re-establishment of services after conflicts. Recommendations pertain to information and understanding, the prevention of violent conflicts, peacekeeping, health-sector responses, and humanitarian responses. "Boxes" within the chapter provide brief discussions of torture, health as a bridge for peace, and child soldiers and issues for health professionals. 5 tables, 1 figure, and 81 references