This Special Issue seeks to cover all geobiological aspects of the upper crust (continental and marine) and we invite contributions with relevance to geomicrobiology, isotope geochemistry, microbial-activity-associated geochronology and related geochemical and hydrochemical proxies as well as presentations on new methods, techniques, and experimental approaches in both the modern and ancient crust. We wish to cover a broad spectrum of environments such as ultra-mafic, mafic, and felsic systems, as well as hydrothermal/geothermal areas and sedimentary successions. We encourage contributions related to scientific drilling programs as well as research from underground facilites and deep drillings related to mining activity or nuclear waste disposal, in addition to studies of exposed ancient crust. Astrobiological implications are also encouraged. Deadline for manuscript submissions: September 1, 2019.