The Vienna Convention on the Law of Treaties (VCLT) contemplates the interpretation of treaties topic in its articles 31, 32 and 33, portraying the frame to be followed by one who is engaged in this difficult endeavor. Tax treaties are, fore and foremost, treaties. Therefore, the VCLT is the leading guideline for their interpretation. The United States has sixty-eight income tax treaties in force. If one logs on any website provider of case-law services and types “tax treaty,” more than six hundred cases will pop up. This paper focuses both on what courts have been doing and on what they could have been doing, according to the VCLT, when ruling about tax treaties, but theorizing an approach to the interpretation of tax treaties is not its intent. Regardless of the inference of Savigny and other jurists that “interpretation is an art” and “cannot be learned and governed by any specific rules,” in accordance with the preponderant point of view, customary international law has developed rules on interpretation of treaties, which are accurately contemplated in the VCLT. Still, the American judiciary does not exactly follow its rules. Nonetheless, the U.S. court decisions that have already applied the interpretation rules of the VCLT are “especially valuable” as substantiation of international law since they are rendered by courts of a nation not a party to the Convention, and their importance is further reinforced because the United States, as the most active treaty-maker in the world, decidedly influences the law applicable to treaties.