This chapter focuses on the needs of hypothetical decision-makers who need to prioritize planned investments in climate change mitigation and adaptation (or both). It caters to decision-makers who may work at a global, regional, or local scale. It begins by explaining why both climate change mitigation and climate change adaptation are now essential, urgently needed human responses to climate change, and why these are now both required if humans are to significantly reduce climate change risks. It warns of potential conflicts between adaptation and mitigation—because actions that are beneficial in one sector, system or region, often have unintended negative consequences for another. The need to design policy portfolios as far as possible in a synergistic fashion is explained, providing examples of potential synergies and conflicts. Hence, a fully integrated assessment of the consequences of potential adaptation or mitigation actions is advisable before decisions are made. For those focusing mostly on mitigation, a section provides advice on the design of mitigation policy portfolios, giving examples of how well-designed portfolios are embedded in sustainable use of land. A final section discusses adaptation policy portfolio design using the UK Climate Change Risk Assessment as an example of good practice.