This paper develops a quantitative open economy framework with dynamics, firm heterogeneity and financial frictions to study the impact of corporate tax reforms targeted at multinationals. The model quantifies their impact on firm selection, production and welfare. Firms draw idiosyncratic shocks, invest in capital, choose optimal financing and select endogenously into selling abroad, through exporting or FDI. I apply this framework to the removal of the U.S. repatriation tax as in the Tax Cuts and Jobs Act. The reform’s impact trades-off two selection effects — more offshoring versus greater U.S. business dynamism. The reform leads to higher U.S. welfare at little cost to the Treasury. A series of exercises illustrate that the novel features of this framework have significant quantitative implications. The reform gives starkly different cross-sectional predictions and lower welfare gains when financial frictions are removed and it is welfare reducing in a static counterpart of the model.