This study deals with some specific problems of Art. 2 (Taxes covered) of the OECD Model Tax Convention, but is not limited to that article. The word "tax" is used not only in Art. 2, but also in the "administrative provisions", in particular, Arts. 24, 26 and 27 of the OECD Model. This study first examines two specific problems regarding Art. 2: whether social security contributions are covered by Art. 2, and the sometimes difficult interaction of Art. 2 with the OECD Model Double Taxation Convention on Estates and Inheritances and on Gifts. The study then considers the meaning of the word "tax" in Arts. 24, 26 and 27. The choice of issues to be studied is largely determined by other international norms which may have an impact on these articles of the OECD Model. The author's conclusion on the objective scope of income tax treaties, however, is of a general nature.