These guidelines were developed by the Centers for Disease Control and Prevention for state and local agencies and organizations planning programs to prevent head injuries among bicyclists through use of bicycle helmets. The guidelines contain information on the magnitude and extent of the problem of bicycle-related head injuries and potential impact of increased helmet use; characteristics of helmets, including biomechanical characteristics, helmet standards, and performance in actual crash conditions; barriers that impede increased helmet use; and approaches to increasing use of bicycle helmets within the community. In addition, bicycle helmet legislation and community educational campaigns are evaluated.