The characterization of fractured reservoirs and fractured geothermal resources requires a thorough understanding of the geological processes involved during fracturing and the rheological properties of the host rock. The presence or absence of mechanical layering within the rock and the mode of failure substantially control the organization and scaling of the fracture system; subsequent chemical alteration and mineralization can either increase or decrease the porosity and permeability. An integration of this understanding using information from outcrop analogues, together with static and dynamic subsurface data, can improve our ability to predict the behaviour of fractured reservoirs across a range of scales. Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs