[en] This paper discusses and contrasts the proposals for an Energy Union in the European Union and its impact on security-of-gas-supply. Based on an examination of historical East-West gas trade and by revisiting energy security concepts, the paper analyzes how problems with dependency on energy imports can be reduced. The paper discusses how the positions of Central and Eastern European countries (CEEC), where security challenges are especially evident, and the positions of countries in Western Europe, where they are less acute, interact and conflicts in making a common energy security policy as part of the Energy Union. The paper argues that the mainly confederative structure of the EU, and diverging national situations, make it difficult to unify positions into an effective common energy policy. However, with the CEEC in the EU, the EU is also changing, and an increased focus on energy security may be accepted. Extended interconnectedness within and to the CEEC appears to be the central issue that would mitigate, albeit not solve, contemporary security-of-gas-supply problems. As it would also bring the internal energy market closer to reality, it could in addition help the Energy Union to become a unifying project merging the interests in the East and the West despite their different security-of-gas supply concerns with Russian gas. - Highlights: •Security-of-gas-supply concerns divides the EU between Central/Eastern and Western Europe in the creation of an Energy Union. •Gas security may be improved by internal measures and better inter-connectedness to and within Eastern Europe, if external relations to Russia will not change. •More infrastructure may help the functioning of a Single Market for energy and make the Energy Union a unifying project between the East and the West.