The study of life in extreme environments is a highly interdisciplinary subject, which helps further the understanding of the biological and biogeochemical processes taking place in various environments on the Earth generally considered hostile to life. Life in extreme environments tells us about the limits of life, and in turn, about the possibility of life beyond the Earth. PLOS ONE and PLOS Biology are delighted to announce a Call for Papers on the topic of Life in Extreme Environments, bringing together studies from different disciplines such as biosciences, geosciences, planetary sciences, oceanography and related disciplines in order to shed light on this crucial topic, and to present this research to the broad readership of PLOS ONE and PLOS Biology. This interdisciplinary topic helps us better understand the biodiversity of life on Earth, and the biological processes, geochemistry and nutrient cycling taking place in many of the Earth’s most inhospitable environments, and enables us to make inferences about the potential for life beyond the Earth. Microorganisms and other life in extreme environments are fundamental agents of geochemical and nutrient cycling, in many of the most poorly understood environments on the Earth. A particular set of challenges is present when studying extreme environments, such as the problem of detecting small cell numbers and slow metabolisms, as well as contamination and false positives introduced during sampling and analysis. We particularly welcome submissions with a strong interdisciplinary focus, and papers seeking to improve methodology for sampling and characterizing extreme environments. The submission deadline for this Collection has been extended to October 25, 2019.