In the United States, many states have sought the objective of uni- formity by enacting the Uniform Division of Income for Tax Purposes Act (UDITPA). In addition, many of those same states have entered into the Multistate Tax Compact (MTC). The salutary objective of both the UDITPA and the MTC is to provide uniform rules for the allocation and apportionment of income, in order to facilitate both compliance and enforcement, as well as to reduce the likelihood of double taxation. The promised uniformity, however, has been at the same time both illusive and elusive. Experience with the UDITPA and the MTC in the United States has demonstrated that a multilateral treaty would not achieve uni- formity amongst the numerous sovereign countries of the world, primarily because there is no paramount supervisory body in the international arena. At the same time, uniformity could be achieved within the United States by pre-emptive federal legislation uniformly interpreted and ap- plied to all of the states. The uniform application of an apportionment formula to distribute the tax base of a multijurisdictional unitary enter- prise would avoid many of the problems of the separate entity approach, producing a fair, equitable determination of the tax base for state income taxes. Part II of this article will examine the treatment of business income of multinational enterprises under tax treaties, and Part III discusses the determination of the tax base of such enterprises. Part IV examines the evolution of the law pertaining to state imposed taxes on, or measured by, the net business income of multistate unitary enterprises, the issues of jurisdiction and the determination of the tax base. Part V addresses vari- ous attempts to achieve uniformity in state taxation. Part VI suggests that in the international setting, the goal of uniformity is unlikely to be achieved by a multilateral treaty, but that within the United States, pre- emptive federal legislation should be enacted.