This thesis explores relations between the European Union and its largest neighbour - Russia, placing emphasis on the energy aspect of their strategic cooperation. Specifically, it is argued that growing reliance on Russian energy supplies may entail certain threats of economic and political nature to the EU. Hence the main objective of the paper is to deliberate on possible explanations of the EU’s policy consisting in further tightening of energy bonds with Russia, despite risks stemming from rising dependence on this state’s energy resources. It is among others analysed whether such stance may derive from lack of reliable alternatives. Specifically, it is considered whether stronger diversification of oil and gas providers, notably intensification of cooperation with the Caspian, North African or the Middle East regions, could help the EU to strengthen the group’s energy security through diminishing the large influence of Russia in this sphere. Further deliberations are devoted to the question whether the EU member states would be likely to reach a consensus on this matter. An alternative explanation of the EU’s stance towards Russia is sought within the overall relations of the two parties. In particular, it is considered whether the EU’s conduct may be explained by the conscious policy aiming at reinforcement of other than energy links and thereby balancing its reliance on Russian resources. The analysis of the abovementioned issues is supported by theoretical perspectives of realism and liberalism, as well as by Barry Buzan’s conceptualization of security, notably his idea of the Regional Security Complexes.