En-ROADS is a transparent, freely-available policy simulation model that provides policymakers, educators, businesses, the media, and the public with the ability to explore, for themselves, the likely consequences of energy, economic growth, land use, and other policies and uncertainties, with the goal of improving their understanding. The simulation, developed by Climate Interactive, Ventana Systems, and MIT Sloan, runs on an ordinary laptop in a fraction of a second, is available online, offers an intuitive interface, has been carefully grounded in the best available science, and has been calibrated against a wide range of existing integrated assessment, climate and energy models.