In this Very Short Introduction Jan Zalasiewicz gives a brief introduction to the fascinating field of geology. Describing how the science developed from its early beginnings, he looks at some of the key discoveries that have transformed it, before delving into its various subfields, such as sedimentology, tectonics, and stratigraphy. Analysing the geological foundations of the Earth, Zalasiewicz explains the interlocking studies of tectonics, geophysics, and igneous and metamorphic petrology and geochemistry; and describes how rocks are dated by radiometric dating. Considering the role and importance of geology in the finding and exploitation of resources (including fracking), he also discusses its place in environmental issues, such as foundations for urban structures and sites for landfill, and in tackling issues associated with climate change. Zalasiewicz concludes by discussing the exciting future and frontiers of the field, such as the exploration of the geology of Mars.