This paper is provided to assist utility regulators, gas and electric utilities, and others in meeting the National Action Plan for Energy Efficiency's goal of achieving all cost-effective energy efficiency by 2025. This paper summarizes the scale and economic value of energy efficiency for reducing carbon emissions and discusses the barriers to achieving the potential for cost-effective energy efficiency. It also reviews current regional, state, and local approaches for including energy efficiency in climate policy, using these approaches to inform a set of recommendations for leveraging energy efficiency within state climate policy. The paper does not capture federal climate policy options or recommendations, discussion of tradable energy efficiency credits, or emissions impacts of specific energy efficiency measures or programs. The intended audience for the paper is any stakeholder interested in learning more about how to advance energy efficiency as a low-cost resource to reduce carbon emissions. All stakeholders, including state policy-makers, public utility commissions, city councils, and utilities, can use this paper to understand the key issues and terminology, as well as the approaches that are being used to reduce carbon emissions by advancing energy efficiency policies and programs.