The MIT U.S. Regional Energy Policy (USREP) Model has been broadly applied to energy and environmental policy analyses.  We provide an overview of the base model, detailed description of the equilibrium structures and main features that drive the dynamic process of the economy growing out to 2050.  Given the common features shared between USREP and the MIT Economic Projection and Policy Analysis (EPPA) model, a large part of the description is drawn from EPPA documentation.  We also extract from previous literatures the description of several features developed for USREP.  The objective of this report is to build a reference point for future development of USREP.  Thus revisions to improve the representation of the U.S. economy and energy market are documented in addition to the base model description.