For more than twenty years, IFP Energies Nouvelles has been developing the thermodynamic library Carnot. While devoted to the origin of the oil and gas industry, Carnot is now focused on applications related to the new technologies of energy for an industry emphasizing decarbonization and sustainability, such as CCUS, biomass, geothermal, hydrogen, or plastic and metal recycling. Carnot contains several dozens of predictive and correlative thermodynamic models, including well-established and more recent equations of state and activity coefficient models, as well as many specific models to calculate phase properties. Carnot also contains a dozen flash algorithms making possible the computation of various types of phase equilibrium, including not only two-phase and three-phase fluid equilibria but also configurations with reactive systems and with solid phases such as hydrates, wax, asphaltene, or salts. The library Carnot has a double role: first, it is a standalone toolbox for thermodynamic research and development studies. Coupled with an optimization tool, it allows to develop new thermodynamic models and to propose specific parameterizations adapted to any context. Secondly, Carnot is used as the thermodynamic engine of commercial software, such as Carbonee, Convergee, TemisFlowe, CooresFlowe or Moldie. Through this software, several hundreds of end-users are nowadays performing their thermodynamic calculations with Carnot. It has also been directly applied to design industrial processes such as the DMXe process for CO 2 capture, the ATOL â and BioButterFlye solutions for bio-olefins production, and Futurole and BioTFuele for biofuels production. In this context, this article presents some significant realizations made with Carnot for both R&D and industrial applications, more specifically in the fields of CO 2 capture and storage, flow assurance, chemistry, and geoscience.