The Massachusetts Green Communities Grant Program (GCP) was created by passage of the Massachusetts Green Communities Act in 2008, which provides funding, tools and technical support to assist local communities in achieving the goal of energy efficiency and greenhouse gas (GHG) emissions reduction. With the growing number of communities designated as GCP participants over the past two years, public focus has increasingly turned towards assessing the relative effectiveness of the GCP compared to other programs. The purpose of this research is to evaluate the relative effectiveness of the Green Communities Grant Program in supporting participating local governments to mitigate and adapt to climate change, especially in the areas of energy efficiency and emissions reduction. The findings are based on comparative case study analysis between participant Green Communities and non-Green Communities with comparable population size. The results of the qualitative analysis indicated that the communities with relatively strong regional planning agency assistance, relatively large planning departments, completed master/comprehensive plans, and memberships in other climate change protection and sustainable development organizations tend to have much better performance in energy efficiency and GHG emissions reduction. The research also provides suggestions for future research and recommendations for other Massachusetts communities that plan to implement energy-efficiency projects and emissions reduction strategies, whether or not through GCP membership.