The lack of effective vaccines for emerging infectious diseases (EID) of limited market potential, such as Chikungunya and Zika, poses a serious threat to human life and prosperity. Research and development (R&D) for new vaccines for EIDs faces two major challenges. The first is R&D preparedness: that is, to advance EID vaccine candidates to the latest R&D stage possible during non-epidemic times, on the basis of any feasible safety or efficacy data. The second is R&D response: that is, to test the clinical efficacy of vaccine candidates rapidly once an outbreak erupts. To overcome these challenges, the Coalition for Epidemic Preparedness Innovations (CEPI) was established in August 2016. Here, we explore why the realisation of CEPI’s mission—preventing outbreaks of emerging infectious diseases from becoming humanitarian crises—is a global public good, and the crucial role R&D preparedness and R&D response play in providing this good. We next examine why providing this global public good requires incentivising involvement and sharing risks with the private sector. Finally, we explore the potential for CEPI to be an agent mobilising shared responsibilities, including key factors that must be addressed in order for CEPI to demonstrate to governments that collective action is the preferred strategy for preventing future epidemics and strengthening global health security.