1. If you do not know what the abbreviations in rule 21.4: Treaties stand for, Table 4 of The Bluebook: A Uniform System of Citation (Columbia Law Review Ass'n et al. eds., 20th ed. 2015) provides full titles of abbreviated treaty sources.
2. To apply rule 21.4, determine whether the U.S. is a party to the treaty.
Sources that answer this threshold question:
3. If you find a cite to the treaty, copy the cite.
4. If the U.S. is a party to the treaty, apply either rule 21.4.5(a)(i) [primarily: bilateral treaties] or rule 21.4.5(a)(ii) [multilateral treaties].
5. If the U.S. is not a party to the treaty, apply rule 21.4.5(b).
Components of a Bluebook-compliant treaty cite:
Bilateral treaty & U.S. is a party:
Convention for the Avoidance of Double Taxation and the Prevention of Fiscal Evasion with Respect to Taxes on Income, U.S.-Austl., art. 1, Aug. 6, 1982, 35 U.S.T. 1999.
Multilateral treaty & U.S. is a party:
Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies art. 6, Jan. 27, 1967, 18 U.S.T. 2410, 610 U.N.T.S. 205.
Multilateral treaty & U.S. is not a party:
Vienna Convention on the Law of Treaties art. 32, May 23, 1969, 1155 U.N.T.S. 331.
Consolidated Version of the Treaty on the Functioning of the European Union art. 122(2), Mar. 30, 2010, 2010 O.J. (C 83) 47.