Energy efficiency of electronic systems has emerged as one of the most important trends in integrated circuits research in recent years. The results of this continued effort are visible in all kinds of electronic functions: DSPs (reaching the 10 μW/MMAC according Gene's law), data converters (the FOM of recent ADCs is approaching 15 fJ/conversion step  (Liu et al., 2010)), power converters (reaching unprecedented efficiencies in ultra-low-power regime) and radios (achieving an energy budget lower than 1 nJ per received-transmitted bit [2,3] (Daly et al., 2010; Mercier et al., 2008)). Exploiting this continuously improving energy efficiency, the progressing battery technology and advances in energy harvesting, miniaturized electronic sensors that do not need to be recharged for their whole operational life and can communicate among them to build up an energy-autonomous system are possible nowadays. A working group has been set up by CATRENE\1 to study the state and the development of these "energy autonomous systems". This paper summarizes the findings of the working group, expanding and updating in this special issue of the Microelectronics Journal on IWASI09 the report written for the proceedings of the workshop  (Belleville et al., 2008). © 2010 Elsevier Ltd. All rights reserved.