This annual report is a composite index that focuses on tracking specific indicators to measure the energy system performance of 125 countries. At its core are 18 indicators defined across each side of the energy triangle: economic growth and development, environmental sustainability, and energy access and security. The report provides a tool for decision-makers to holistically benchmark nations’ energy systems. It aims to support governments and other stakeholders along the energy value chain in identifying the relative performance of elements of their energy systems, in order for best practices to be diffused more widely and poor practices targeted. The report also provides a transparent and easily comparable set of measures that can help track progress and open new perspectives on the specific challenges faced by individual countries in each region. Past reports include 2014 and 2013.