I explore the effects of the implementation of the two U.S. cap-and-trade policies on carbon dioxide (CO2) emissions for the two regions in which the policies are active as well as the regions on their respective borders. The cap-and-trade policy is a market-based approach to reduce emissions by capping the total amount of emissions produced and allowing emission producing entities to trade emission allowances on an open market. The two active cap-and-trade policies in the United States are the Regional Greenhouse Gas Initiative (RGGI), located in the northeastern United States, and in California, which differ in design, scope, and duration. I use a difference in differences design to analyze the change in CO2 emissions in the states effected by the policies relative to the rest of the country. I find that the RGGI policy has not reduced CO2 emissions in comparison to the rest of the non-policy states but only the California emission trading system has yielded a statistically significant decline. The results also find that the there is no evidence to suggest different changes in CO2 emissions in the states bordering both regions in which the policies are in place.