Findings of my dissertation contribute to three bodies of literature - in the first place to the burgeoning field of influence in international relations, secondly to the conflicted nature of energy security, and finally to the literature on policy choices during transition in the natural gas sector. First, conceptual confusion about what influence in international relations is, how to measure it and analyse, persists in the literature. This is a result of the interplay of a number of factors. I argue, that the concept of influence is as important as it is ambiguous in international relations. The same applies to the notion of power. Moreover, the two concepts are inherently connected, however, one defines them, and they are even equated by many, at least in certain contexts, even though power-as-influence should be distinguished from power-as-control. Conceptually, I introduced the process tracing method to assessing historic developments of influence by analysing geographical proximity, existing pipeline infrastructure, ruling elites’ relations with Russia and the EU requirements on the stance of Visegrad Countries. To my best knowledge, this has not been done before. Second, energy security resulted in more than three dozen mainstream definitions available in the energy security literature and additional meta-literature on the classification of energy security definitions and conceptualizations. My contribution to the energy security literature in this context is refocusing the concentration from a prescriptive conceptual approach to energy security which has been preoccupied with finding the right definition, to a conceptualization of energy security grounded in empirical observation and guided by a descriptive approach. Instead of defining what energy security ought to be, I provide empirical observations. Not everything that governments prioritize and do, which pertains to energy, is energy security. Contrary to the expectations of the literature, governments often prioritize other aims than security, even in the objective lack of sufficient security. Additionally, I have enriched literature by introducing the quantitative measure of links of government officials to the previous regime, linking the problem of transitional policies to energy security, which is particularly applicable to understanding of security in general, and energy security in particular during times of transition from totalitarian regimes towards more open and pluralistic ones. The broader theoretical contribution of this dissertation consists of finding the definition for influence in international relations, also finding an argument for reframing the energy policy debate by bringing back domestic politics, and contributing to understanding of policy prioritization during the transition in the natural gas sector. By providing an explanation for the variation and timing of domestic responses to the structural position of gas import dependence over time in countries in transition I have also contributed to the broader research field of domestic responses to comparable international conditions. The analytical framework presented in the research could be used when applied to other cases within this understudied group of countries. The lack of theoretical background in the natural gas security problems has wrought a place where, in most cases, the descriptive analysis completely rules the debate on the role that natural gas resources play in foreign policy.