Abstract: Taxation and trade are governed by two very different sets of international agreements. The bilateral tax treaties, which originated in the 1920s, do not, for example, contain the rule-oriented dispute-settlement procedures of the multinational trade treaties, which have developed since World War II. In this article, Professor Warren analyzes the constraints imposed by the two sets of agreements on a country's freedom to use its income tax to discriminate against international commerce. His principal conclusions are that the current distinction between permissible and impermissible discrimination is incoherent and that the pre-World War II international tax regime is in need of fundamental reexamination.