In 2008 the CATRENE Scientific Committee established a Working Group on Energy Autonomous Systems (EAS) with the mission of writing a White Paper on this topic. The approach was to gather European experts from academia and industry representing various areas related to EAS in order to: i) define the field, ii) review the current state-of-the-art, iii) discuss the future impact of EAS technologies on the electronics industry and on society at large, iv) identify Europe’s strengths and weaknesses, and v) formulate recommendations with respect to public initiatives, efficient research and education. Special care was devoted to the boundaries within this multidisciplinary scientific field. One of the main outputs of this study has been the preparation of a Technology Readiness Levels (TRLs) document for each of the areas of the report: energy harvesting and sources, ultra low-power systems and power management. These TRLs make a forecast of existing technologies by assessing the present state of development as well as a projected timeline for future developments in the next 5 and 10 years, respectively.