We analyze the cross-country spillover effects of corporate tax reforms. Combining firm-level evidence on the 2017 U.S. Tax Cuts and Jobs Act (TCJA) with a quantitative general-equilibrium model, we show how multinational enterprises (MNEs) propagate local policy shocks throughout the global economy. Our framework emphasizes three properties of intangible capital: non-rivalry, mobile ownership, and technology spillovers. We find the TCJA generated positive outward spillovers: First, it boosted U.S. MNEs’ intangible investment, raising their foreign subsidiaries’ output. Second, it increased tangible investment of foreign MNEs’ U.S. subsidiaries, incentivizing them to expand intangible investment at home. Conversely, a Global Minimum Tax (GMT) in the rest of the world generates negative inward spillovers for the United States. It raises the effective tax rate on U.S. MNEs’ foreign income, depressing their intangible investment, while simultaneously reducing foreign MNEs’ intangible investment and thus their U.S. subsidiaries’ output. These findings illustrate the complex trade-offs between tax-base protection and real economic activity in an interconnected policy environment.