In this topical, we will explore chemical engineering aspects of subsurface engineering processes. Fossil fuels will continue their dominant roles over the next several decades, even as the world transitions to more renewable energy choices with reduced carbon emissions. Efficient production, transportation and processing of these conventional energy resources will continue to be important. Understanding multicomponent, multiphase, high-pressure thermodynamics and flow in highly complex geologic formations is necessary in order to optimize energy and fuels production. These fundamental scientific aspects are also relevant in the study of sequestering carbon dioxide in underground formations, in natural and engineered geothermal systems and in underground thermal treatment of carbonaceous materials. The purpose of this topical is to highlight these scientific and engineering aspects of complex subsurface engineering processes in six diverse, yet interconnected sessions.