As the increasing share of Renewable Energy Sources (RES) gradually replaces energy production from fossil fuels (coal, oil, natural gas), the national energy system is unavoidably tackling an energy transition. As the role of energy is critical for countries’ prosperity, the energy transition is evaluated with respect to the Energy Trilemma, defined as the challenge of a secure, affordable and environmentally sustainable energy supply; therefore, the Energy Trilemma dimensions include Sustainability, Equity and Security. In this context, the definition of scientific methods to quantify the monitoring of the evolution of the energy transition is a topic of growing importance. However, as the Energy Trilemma dimensions are not uniquely defined or measurable, numerical indexes must be defined and aggregated for the purpose.