Over the coming months President Trump will decide on whether to adopt the tax reform proposed by House Republicans. This decision could have a historic impact on international corporate taxation, with wide-reaching yet unpredictable knock-on effects on trade, exchange rates, industrial competitiveness, investment decisions, and tax revenues. If the House Republican plan is implemented, it would make the United States an outsider in the global system of corporate taxation. It would fatally undermine the OECD's efforts to combat the offshoring of profits with coordinated tax policies. Furthermore, it would incite industrialised nations to enact protectionist countermeasures.