The purpose of this article is to introduce to the international lawyer the somewhat different set of categories (e.g., residence and source rather than nationality and territoriality) employed by international tax lawyers, and explain the reasons for some of the differences. At the same time, it attempts to persuade practicing international tax lawyers and international tax academics that their field is indeed part of international law, and that it would help them to think of it this way. For example, knowledge of the Vienna Convention on the Law of Treaties would help international tax lawyers in interpreting tax treaties, and avoid some common mistakes.