Background The library includes pre-developed messages for 23 different hazards, across three phases of the disaster lifecycle (Preparedness, Response, Recovery), for three different channels (Twitter, Facebook, and Instagram). Some messages may be used without significant modifications, but because every emergency and its impact on public health is unique, some will serve as points of departure for users who communicate via social media platforms during disasters. Messages are organized for easy viewing by hazard and, within each hazard, by phase of emergency response. The messages were reviewed by individuals with expertise in content areas and in public information and risk communication from the following organizations: Centers for Disease Control and Prevention, Radiation Studies Branch National Public Health Information Coalition (NPHIC) Association of State and Territorial Health Officials (ASTHO) National Association of County and City Health Officials (NACCHO) State Health Departments New Mexico Department of Health Oregon Health Authority Pennsylvania Department of Health Local Health Departments Bucks County Department of Health Chester County Health Department Philadelphia Department of Public Health Local Emergency Management Agencies Chester County Department of Emergency Services