Bahrain and Iceland deposited their instruments of accession to the Vienna Convention on the Law of Treaties on 24 and 25 September 2025, respectively. The Convention, adopted in 1969, is the foundational framework for how treaties are drafted, interpreted, amended, and terminated, including tax treaties. It codifies customary international law and is widely regarded as the "treaty on treaties". The Convention is effective for Bahrain and Iceland on 24 and 25 October 2025, respectively.