GOA-ON is a collaborative international network to detect and understand the drivers of ocean acidification in estuarine-coastal-open ocean environments, the resulting impacts on marine ecosystems, and to make the information available to optimize modelling studies. The network is fundamental to providing early warning of the impacts of ocean acidification on natural ecosystems, wild and aquaculture fisheries, coastal protection, tourism and local economies. The network provides key input to communities, industry and governments seeking to develop action plans, best practices, and mitigation or adaptation strategies to address ocean acidification impacts. GOA-ON is organized at the global scale, reaching out to members all over the world who are working at local through global scales. Our mission is globally based for three important reasons: 1. We need information and data products that can inform policy and the public with respect to ocean acidification and implications for the overall ecosystem health (status) of the planet; 2. Ocean acidification processes are occurring at global scales; therefore, we need to go beyond local measurements and observe ocean acidification globally in order to understand its drivers correctly; 3. Insufficient observations and understanding impede the development of robust predictive skills regarding ocean acidification and impacts. While we need enhanced coverage at local scales, successful international coordination of these observations will allow for nesting of these local observations within a global context.