The past two years have seen rapid development of climate and trade policy, including the announcements of an EU Carbon Border Adjustment Mechanism (CBAM), U.S. congressional proposals for border carbon adjustments (BCA), the Global Arrangement on Sustainable Steel and Aluminum (GASSA), and the G7’s climate club. More approaches are likely to proliferate from this Congress, the administration, and international partners. This primer explores why momentum for border carbon adjustments is accelerating now and reviews proposals in various stages of implementation and consideration.