As a result of increasing globalisation taxpayers are much more mobile internationally than they once were. This not only makes it harder for revenue bodies to accurately determine the correct tax liabilities of their taxpayers: it also makes tax collection more difficult. However, national revenue bodies only have jurisdiction within the borders of their own country under the principle of fiscal sovereignty. In general the authorities of one country will not assist with the recovery of taxes due to another country, a principle known as the “Revenue Rule”, unless they have entered into a bilateral, regional or multilateral agreement that provides for mutual assistance in the recovery of tax claims. If national measures are exhausted in a cross-border case where the taxpayer resides abroad and/or owns assets in another country, the tax collector has to seek recourse abroad.