Energy supply security has been a crucial energy policy issue for CEE countries at least since the natural gas supply disruptions of 2006 and 2009. This book argues that energy security plays a generally more important role within the CEE region than issues related to climate change. However, this chapter evaluates the interplay between ideas, institutions and the material nature of energy systems in the development of energy policy. In doing so it also highlights the social construction of energy security, demonstrating that energy security is not self-evident or correlated within the CEE region with dependency on energy imports from Russia. Individual CEE countries perceive energy supplies as a security issue to a different extent, identifying the source and extent of insecurity or risk differently, and supporting different policy responses as a result. While some countries, for example, Hungary or Bulgaria, have tended to perceive Russian energy as a means to guarantee energy security, others – most notably, Lithuania and Poland – consider energy security to be one of their main policy issues and imports of Russian energy as one of the main threats to this.