Evaluating the impact of proposed changes to the law requires predicting how people’s behavior will change in response to this or that policy change. These predications are made using microsimulations. Researchers compile data from a representative sample of the population, run models that estimate what those individuals will do in response to changes in, say, the tax code, and then aggregate the results. This is a traditional tool not just for economists but also for the study of traffic, finance, epidemiology, and crowds. The problem with microsimulations, however, is that they are computationally unwieldy. Running a sophisticated model requires lots of time and computing power. Funds from this grant support efforts by Robert McClelland at the Urban Institute’s Tax Policy Center (TPC) to take the next big step in microsimulation by harnessing the power of cloud-based computing. McClelland will move the TPC’s existing tax policy evaluation microsimulation models to the cloud, allowing the models to both be run faster and to allow multiple simulations to be run at once. This will make it routinely practical, for example, to see how robust results are to changes in parameter choices, to evaluate many different policy options and see which works best, and to handle nonlinearities due to thresholds in the tax code where different rules kick in or out. Basic statistical tasks—like obtaining variances, building confidence intervals, or testing hypotheses—should run in a matter of hours rather than months. These new capabilities will greatly enhance how useful TPC’s models are for rapidly understanding proposed changes in the tax code. The TPC team will then test these new capabilities by investigating three specific research questions: How does uncertainty in growth rates and recession timing affect projected tax revenues? How does sampling variation affect model behavior? And how can tax policies improve distributional outcomes without reducing revenue? Lastly, TPC will also launch an interactive website where the public can explore and visualize tax plans of their own design in real time.