This report introduces stakeholders to the concept of a Clean Energy Standard (CES), a type of electricity portfolio standard that would set aggregate targets for the level of clean energy that electric utilities would need to sell while giving electric utilities flexibility by: (1) defining clean energy more broadly than just renewables, and (2) allowing for market-based credit trading to facilitate lower-cost compliance. As a concept, a CES builds on the successful experience of the majority of states that have implemented renewable and alternative energy portfolio standards and draws on a history of federal policy deliberation regarding national electricity portfolio standards. The report explains how a CES works, describes the benefits that a CES can deliver, and explores federal and subnational options for CES policies. It also explores some of the nuances of CES policy design and the implications of different design choices. This discussion can help state and federal policymakers, utility regulators, and other stakeholders decide whether a CES is an appealing option and help state stakeholders understand the potential impacts of a federal CES on their states so that they might formulate and communicate federal CES policy design preferences.