Why do nation states participate differentially in International Environmental Agreements (IEAs), and how can we achieve greater international environmental cooperation through enhanced participation in IEAs? Drawing upon the basic tenets of Realism and Liberalism, and using regression analyses, this study presents the Incentives-Capabilities model for explaining state participation in IEAs. The model highlights the importance of both IEA design and state capabilities to engage effectively in international environmental cooperation. While there may be domestic structural constraints that limit a state’s capability of ratifying an IEA (e.g. low human development, high foreign aid dependency, high levels of corruption, etc.), the design of IEAs, through a proper structuring of incentives, may make ratification a choice that furthers the national interest of the state, and thus result in successful participation. This book theorizes international environmental cooperation based on the concepts of an international system structured by global interdependence and interconnectedness, and through national interest calculations built on the twin objectives of enhancing domestic capabilities (through resources transfer or market advantage, for example) as well as maintaining development trajectories. A key policy outcome of this study is that effective global environmental protection is premised upon strategies for furthering human development, equity, and sustainable development.