The purpose of this dissertation research is twofold: to explain why and how emerging great and middle power countries established new intergovernmental organizations (IGOs) and to consider implications for changing global norms and practices of sustainable development. Rather than focusing on either the international context or domestic motivations, this study explains the phenomena of IGO establishments by incorporating factors and strategies at both levels. This study offers two arguments: that emerging great and middle power countries created IGOs as a response to a combination of different international and domestic factors, and that, contrary to initial speculations, this array of new IGOs poses little threat to the existing norms and practices of pre-existing institutions. In this study, three detailed case studies on the Asian Infrastructure Development Bank, the New Development Bank, and the Global Green Growth Institute and their comparative assessment are presented. The findings from this research point to the broader debate on international relations theory investigating the utility and impacts of international cooperation and institutions, international environmental governance, and the effectiveness of international regime complexity and fragmentation. The urgency of developmental and climate challenges, as well as the lasting impact of development projects and policy implementation, makes this research project ever more relevant.