This guide has been developed as part of the Chatham House Centre on Global HealthSecurity project Strengthening Data Sharing for Public Health. Sharing public health surveillance data enables regional collaborations, capacity strengthening, and insight into public health system performance, leads to overall improvements in risk management, and enhances public health responsiveness. Informal data sharing arrangements can often produce the desired public health outcome and should be couraged where appropriate. Sometimes, however, more formal agreements are required. This guide is intended to facilitate both informal and formal data sharing and to be used when a need to share public health surveillance data has been identified or when obstacles to sharing have been encountered. It aims to help create the right environment for data sharing, to facilitate good practice in addressing technical, political, ethical, economic, and legal concerns that may arise, and to ensure to the greatest extent possible that any benefits arising from the use of the data are shared equitably.