State health agencies are asked to do a big job. With the advent of an increased focus on bioterrorism preparedness, and the emergence of diseases such as West Nile Virus and SARS, the job is becoming bigger. Yet health agencies still have responsibilities for more traditional concerns, since these problems remain threats to the public. State health agencies can improve their reach and effectiveness by working with other state agencies, local agencies, and private organizations. Offices and units within state public health agencies can do their work more effectively by collaborating in ways that serve all their agendas. This publication will present case studies in which state health agencies have collaborated internally and with other agencies and organizations on traffic safety issues, including child passenger safety, prevention of driving while intoxicated, pedestrian and bicycle safety, and graduated licenses for new drivers. These case studies hold important lessons about the value of collaboration?both within agencies and among agencies?and provide examples for states to consider. All of the collaborations presented in this publication helped advance the cause of injury prevention, but many of them did more. These programs: (1) created opportunities for the public to improve cardiovascular health and prevent obesity by integrating walking and bicycling into their everyday lives; (2) improved health services for underserved populations, including migrant workers, special-needs children, and low-income families; (3) helped police agencies enforce laws more effectively and create programs to prevent violation of child passenger safety, seat belt, and drunk driving laws; and (4) integrated public health concerns into improvements in the transportation infrastructure in ways that create healthier and more livable communities. Collaborative programming can also protect scarce public dollars by eliminating duplication of efforts, leveraging resources, and mo coisks they prevent. Investment in prevention lowers the public bill for emergency services and uncompensated medical care. It reduces public and private insurance costs and private medical costs, and decreases lost work-time and needless pain and suffering.