International business taxation has become the object of debate in recent years. The allocation of taxing rights between residence and source countries is challenged. Time-honoured rules which address different types of business profits, like sales and services, royalties and interest, in different ways, are put to the test. Profit attribution under the arm’s length principle faces the alternative of formulary apportionment. Moreover, international tax competition takes its toll: while some countries exert their tax jurisdiction as far as possible, other countries are no longer willing to tax capital income at all cost and prefer an attractive tax environment for investors. This (two-part) article analyses the value of legal and economic principles for international tax coordination and proposes a “second-best approach”, which leaves domestic tax systems as they are and tries to do away with discontinuities under international taxation, thus avoiding arbitrary results which lead to inequity, inefficiency and tax arbitrage.