This article recommends the key design elements of US climate law. Much past environmental law has suffered from four design problems: fragmentation, insensitivity to tradeoffs, rigid prescriptive commands, and mismatched scale. These are problems with the design of regulatory systems, not a rejection of the overall objective of environmental law to protect ecosystems and human health. These four design defects raised the costs, reduced the benefits, and increased the countervailing risks of many past environmental laws. The principal environmental laws successfully enacted since the 1990s, such as the acid rain trading program in the 1990 Clean Air Act (CAA) Amendments and the 1996 Safe Drinking Water Act amendments, were consciously desig...