Every state in the United States has adopted laws or policies to address climate change, either explicitly or indirectly through energy regulation, transportation-related initiatives, or energy building codes. Innovative state laws and policies have proven remarkably effective in reducing GHG emissions both quantitatively and as a percentage of state GDP. Broadly speaking, states understand that climate change is a global phenomenon that must be addressed nationally and internationally. Inevitably much GHG emission reduction and adaptation to the adverse consequences of climate change falls on states to implement because of their local powers to regulate utilities, land use, building codes, transportation, taxation, environmental programs, agriculture, and other areas of economic activity. This chapter provides a comprehensive analytical review and categorization of these initiatives. It also reviews the legal and policy obstacles that states face in implementing climate policies, as well as the ancillary benefits states stand to reap from their climate change policies. Measures include climate action plans, greenhouse gas (GHG) emission targets,GHG inventories and registries, carbon caps and trading, and offsets for power plants. Many states regulate the electricity sector in ways designed to reduce GHG emissions, such as public benefit funds, green pricing, net metering, renewable portfolio standards, and energy efficiency resource standards. States have adopted a broad range of regulatory initiatives and financial incentives for renewable energy and energy efficiency, and in their agricultural and transportation sectors. Many states are preparing for the adverse effects of global warming by developing climate change adaptation plans. The scope of state legal and policy initiatives has been truly remarkable; it is sufficiently significant to warrant serious attention by any lawyer or policy-maker working in the field.