The climate change is one of the most urgent problems the contemporary world has to face. Having adopted the highest emission reduction target of all industrialized countries, the European Union perceives itself as a frontrunner in the battle against global warming, however, being concerned about the pace of climate change environmental social movements call on the EU to take on more ambitious goals. This thesis examines the role of environmental social movements in the decision-making procedure of the European Union. It demonstrates the multiple points of access to EU institutions as those directly involved in the decision making process. The paper follows the assumption that environmental social movements exert a perceptible influence on the direction of the environmental policy formed within the European Union. Therefore, the advocacy work of two environmental organizations on climate change issues is analysed in terms of their influence on environmental policy outcomes. This thesis’ core interest is to evaluate the extent to what environmental social movements can actually influence the European decisionmaking. The analysis of the aforementioned issues is supported by a theoretical framework comprising of the Theory of Collective Action, Resource Mobilization Theory and Rational Choice Theory.