The first chapter develops and calibrates a dynamic equilibrium model with heterogeneous firms to study the impact of removing the U.S. corporate repatriation tax. I study the impact of the policy reform on firm investment, capital structure, payout policy and tax revenues. Firms in the model make both intensive and extensive margin choices regarding supplying foreign goods markets. I calibrate the model to U.S. data and then run a counterfactual where the repatriation tax is removed. The results show that aggregate U.S. firm productivity rises and more U.S. firms operate as multinationals. Domestic and overseas production by U.S. firms rise and firms borrow more and pay larger dividends to shareholders. These effects on firm variables are coupled with a rise in U.S. Government tax collections and a 0.79% increase in U.S. welfare.

The second chapter studies the transmission of U.S. fiscal policy changes to its major trading partners. In particular, I study the impact of removing the U.S. corporate repatriation tax on foreign tax policy. A two-country model with heterogeneous U.S. and foreign firms is developed and calibrated. The Foreign Government in the model solves a Ramsey taxation problem whereby it optimally chooses domestic corporate and personal tax rates. I run an experiment in the model whereby the repatriation tax is removed. The U.S. reform encourages more FDI by U.S. firms in the Foreign Country. I find that the Foreign Government chooses to decrease its domestic corporate tax rate so as to complement the U.S. policy change and further incentivise domestic investment.

The recent U.S. tax bill removed the "repatriation tax". However, policymakers are concerned that doing so may lead firms to shift more of their earnings to low tax haven nations, thereby putting downward pressure on Federal tax collections. The third chapter develops and solves a model of a multinational firm, who has the option to shift its earnings to a low-tax haven nation. Given the behaviour of the multinational firm, the haven nation solves a Ramsey optimal taxation problem, which involves choosing corporate and personal tax rates. I calibrate the model to a U.S. multinational that shifts its earnings to Bermuda: the classic example of a tax haven. Using the model, I find that if the U.S. moves to a territorial tax system, Bermuda will optimally respond by choosing a positive corporate tax rate, which will lead to a decrease in the earnings shifted by U.S. multinationals.