Ensuring energy security is one of the main objectives of energy policies of many countries worldwide. In this regard, this thesis proposes a metric to evaluate the security of energy systems under medium-to-long term energy scenarios generated by the energy system optimization model TEMOA??Italy. Such a metric consists of an index covering several dimensions of energy security, encompassing the security of energy supply and the internal reliability of the system. Among these dimensions, the inclusion of the supply risk of critical raw materials represents a novelty compared to the existing literature. It enables to account for the possible risks due to the disruption of the minerals supply chains.