Editors' Summary: The two leading broad-based climate change bills in the U.S. Senate are America's Climate Security Act of 2007 (Warner-Lieberman Bill) and the Low Carbon Economy Act of 2007 (Bingaman-Specter Bill). In this Article, Prof. Kenneth R. Richards and Stephanie Hayes Richards examine the most important differences between the two bills, comparing the strengths and weaknesses of each. They make recommendations regarding the bills' emissions targets, cost containment measures, regulation methods, offset and credit provisions, allowance allocation, use of auction revenues, and general strategic approach. Attention to these issues will help the Senate create a more effective U.S. climate change policy.