Glacial systems in the form of glaciers and ice sheets are important actors in Earth's water cycle and climate. Improving our understanding of their structure and functionality is of considerable importance, and glaciologists have tended to apply a purely physical perspective to the study of glacial systems. However, a novel paradigm of glaciers and ice sheets as Earth's largest freshwater ecosystems is being supported by studies revealing the abundance, activity, and diversity of life in glacial ecosystems and the importance of glacial systems in global biogeochemical cycles. Nevertheless, while the importance of microbial activities in shaping their habitats and influencing landscape-scale processes is well recognized elsewhere in our biosphere it has hitherto been overlooked in glacial systems. Here, the potential for several discrete microbial processes to interact with mass balance and landscaping in glacial systems as part of a ‘germ theory’ of glacial systems is identified. These processes range from microbial biocatalysis of ice crystal formation and structure, albedo reduction by microbial assemblages at the ice–atmosphere interface to microbe-mediated mineral weathering at the rock–ice interface. Integrating these microbial processes with abiotic, physical processes in a framework of microbial glaciology will be required to understand the extent and significance of microbial influences upon the properties of glacial systems. Furthermore, adopting a microbial glaciology approach also complements existing physical and chemical approaches to glaciology to understand how glacial systems respond to our warming climate.