The TOUGH (“Transport Of Unsaturated Groundwater and Heat”) suite of software codes comprises multi-dimensional numerical models for simulating the coupled transport of water, vapor, non-condensible gas, non-aqueous phase liquid, and heat, with coupling to geomechanics and reactive transport, in porous and fractured media. The TOUGH codes were originally developed at the Lawrence Berkeley National Laboratory (LBNL) beginning in the early 1980s primarily for geothermal reservoir engineering. The TOUGH family of codes has grown in capability to address a wide range of application areas. The TOUGH codes have a relatively large user base of scientists and engineers at universities, government organizations, and private industry around the world. The main application areas of the TOUGH codes are geothermal energy, geologic carbon sequestration, nuclear waste disposal, hydrocarbon recovery including gas hydrate deposits, groundwater remediation, vadose zone hydrology and critical zone processes, as well as other geological and engineered systems that involve coupled thermal, hydrological, geochemical, and mechanical processes in permeable media. The TOUGH suite of simulators is continually updated with new equation-of-state (EOS) modules, refined process models, and high-performance parallel implementations and currently includes TOUGH3, TOUGH+, TOUGH+Hydrate, TOUGHREACT, TREACTMECH, and iTOUGH2.