Geothermal energy is heat that is generated from within the Earth’s core and due to the decay of radioactive isotopes. To access geothermal energy, drilling a few kilometres (typically 1-5 km) into the subsurface of the Earth’s crust is necessary. Conventional geothermal energy resources are most commonly accessed near volcanic regions and deep sedimentary basins that host hydrothermal (hot water and/or steam) reservoirs. Research and development into unconventional geothermal resources are being commercialized as well, such as utilizing wastewater from oil and gas production, or extracting heat directly from deep, hot rocks using closed-loop borehole heat exchangers. The accessible heat in the subsurface can be used to generate electricity (>80°Celsius) or for low-carbon heating (<80°C) applications.