The increasingly complex nature of transboundary environmental problems, and the risks associated with such problems, present policy makers worldwide with the challenge of designing an effective environmental governance system with a global reach. Environmental governance today consists of a mix of international and domestic law and regulations and private standards, with traditional forms of direct regulation operating in parallel with market-based and suasive instruments. The synergies between states and private actors on the international and domestic plane, and their resulting impact on global environmental governance, have resulted in a great deal of academic literature, but less attention has been paid to the interaction of different regulatory and private instruments at international and domestic levels. This book addresses the crucial question of whether “smart” combinations of instruments at different levels of governance can be found that can more effectively fight against transboundary environmental harm. This book analyzes the concept of smart mixes by discussing the various types and mixes of policy instruments and by addressing how and why particular mixes emerge. In addition, the book identifies what makes a particular mix of instruments “smart” and uses specific case studies relating to the sectors of climate change, forestry, fisheries and oil pollution.