The article analyses how responsible decision makers (Members of the Parliament and employees in the Governmental institutions) adopt their decisions on the issues concerning energy security of Lithuania. The article is based on a constructivist security approach. The article explores what the main challenges and threats to Lithuanian energy security are, as identified by responsible decision makers. The article analyses how the concept of “energy security” is perceived by responsible decision makers. Additionally, the article identifies the groups that most influence the positions of the responsible decision makers. Finally, it is stated that energy nationalism dominates the thinking of responsible decision makers, which is perceived as a way to increase energy security