This paper examines the cost of a range of national, regional and global mitigation policies and the corresponding incentives for countries to participate in ambitious international mitigation actions. The paper illustrates the scope for available instruments to strengthen these incentives and discusses ways to overcome barriers to the development of an international carbon price, based on the quantitative assessment from two global and sectorially-disaggregated CGE models. Key step towards the emergence of a single international carbon price will most likely involve the phasing out of subsidies of fossil fuel consumption and various forms of linking between regional carbon markets, ranging from direct linking of existing emission trading systems to more indirect forms through the use of sectoral crediting mechanisms. The paper discusses regulatory issues raised by the expansion of emission trading and crediting schemes as well as the complementary contribution of non-market based instruments such as the imposition of technical standards and R&D policies. Finally, the paper emphasises the important role of international transfers, not least to overcome the relatively strong economic incentives in some countries to free ride on other regions mitigation actions. While they can take various explicit or implicit forms, transfers made primarily through market mechanisms, for instance via the allocation of binding emission reduction commitments across countries, would be most cost-effective.