The prices assumed, for the purposes of calculating tax liability, to have been charged by one unit of a multinational company when selling to another (foreign) unit of the same firm. Firms spend a fortune on advisers to help them set their transfer prices so that they minimize their total tax bill. For instance, by charging low transfer prices from a unit based in a high-tax country that is selling to a unit in a low-tax country, a firm can record a low profit in the first country and a high profit in the second. In theory, however, transfer prices are supposed to be set according to the arm’s-length principle: that they should be the same as would be charged if the sale was to a business unconnected in any way to the selling firm. But when there is no genuinely independent market with which to compare transfer prices, what an arm’s length price would be can be a matter of great debate and an opportunity for firms that want to lower their tax bill.