R interface to the open source United States ENergy SYStem (USENSYS) optimization model with alternative regional configuration, technological options, and data sources. The package provides functions to choose the model configuration and the data from the list of available options, design technologies, processes, policies, and define scenarios, run the model, store and analyze the results. The model is based on the energyRt package and uses Python/Pyomo or Julia/JuMP or GAMS as the optimization