The possibility of ensuring the energy needed by a country is a fundamental requirement for the economic growth and social welfare of that country. The fulfillment of this need is particularly challenging for those countries that are characterized by a low level of energy self-sufficiency. The evaluation of energy security needs to consider different dimensions and is of the utmost importance as a benchmark to conceive and implement different policies. The assessment of the level of security should rely on science-based models that are able to track the rapidly evolving geopolitical scenarios, and to provide detailed information and quantitative indexes to policy decision makers. In this paper, an overarching methodology is outlined to evaluate energy security, in which its external and internal dimensions are considered and integrated: the security of the energy supply from abroad (external) and the security of national energy infrastructures (internal). Attention is then focused on the external dimension, and two indexes are defined, by means of a probabilistic approach, in terms of the expected value of supply and economic impacts. The methodology is then applied to the Italian case, considering different geopolitical scenarios, and conclusions are provided about the energy security of the country. (C) 2017 Elsevier Ltd. All rights reserved.