This book examines the critical role of communication in advancing knowledge and participation in the governance of global public goods (GPG). Central to any theory of GPG is the role of information, as raising awareness requires creating credible messages and narratives. The book highlights the importance of agency, understanding actors, their interconnections, and how they negotiate and govern GPG. The book argues for a nuanced understanding of democracy, suggesting a broader interpretation that prioritizes public deliberation and reflection. Key premises include the necessity of institutional legitimacy, active citizen participation, structured partnerships, and transparent communication channels for sustainable development. The book underscores that communication is fundamental to change processes, sustainable citizenship, and the realization of human rights, including the right to information and freedom of expression. By doing so, it advocates for an eighteenth Sustainable Development Goal: responsible communication. The book will appeal to students, scholars, and researchers of international relations, communication, and public policy, as well as to policy-makers and professionals at international organizations, think tanks, and NGOs seeking theoretical foundations for communication strategies and stakeholder engagement practices.