Social scientists should be more deliberate in how they define and measure government efforts to reduce greenhouse gas emissions. The authors highlight key distinctions among three dimensions of climate policy: the commitments made by governments, the actions that governments take, and the outcomes they produce. In turn, the authors detail the challenges of measuring these dimensions, and discuss the tradeoffs of alternative measurement strategies, including how well they meet the accepted standards for measurement validity. The authors also identify promising avenues for further research.