Summary Recent research at the frontiers of environmental microbiology has profoundly altered our perspective on the limits of life. Prokaryotic cells in the deep terrestrial or marine sub-surface comprise a majority of all living microorganisms on Earth. How is it possible to maintain complex cell functions at an energy flux that barely allows cell growth over tens to thousands of years? Do these organisms have properties beyond our current understanding of microbial life? To address these questions, we organize an International Workshop on Microbial Life under Extreme Energy Limitation. An important aim of the workshop is to stimulate dialog, new thinking, and new approaches by bringing together researchers from diverse disciplines, and engaging the interest of students and young scientists.