Since its Company Tax Communication of 2001, the European Commission has been promoting a comprehensive harmonization of corporation taxes within the Internal Market on the basis of consolidation and formulary apportionment of the profits of cross-border enterprises, both in the form of a Home State Taxation (HST) and of the Common Consolidated Corporate Tax Base (CCCTB). This study aims to assess whether this approach represents a viable alternative to the arm's length standard currently applied in international tax law. The study comprises four parts. First, a theoretical concept of formulary apportionment is presented in order to define the role that formulary apportionment could take in the area of profit allocation within the Internal Market. This is followed by an in-depth evaluation of the practical experiences of four jurisdictions (United States, Canada, Switzerland and Germany) with formulary apportionment at the subnational level. Next, a comprehensive proposal for harmonization on the basis of consolidation and apportionment is developed, using the insights from the foregoing theoretical considerations and comparative analysis. The book concludes with an overall analysis of the merits and drawbacks of the proposed model for harmonization which suggests that consolidation and formulary apportionment could indeed represent a workable solution to numerous problems of corporate taxation within the Internal Market.