Annex 1 to the Treaty assigns each state to one of six geographical regions for the purpose of determining Executive Council composition, in accordance with paragraph 28 of Article II. That paragraph assigns a specific number of seats to each of the six geographical regions, and paragraph 29 of Article II sets forth the procedures whereby each regional group must designate States Parties within that regional group for election to the Executive Council.

The listing of states in Annex 1 is designed to be comprehensive and includes not only those States that participated in the negotiations, but also all other states that are generally recognized as "states" under international law. Nevertheless, in the event that it becomes necessary, Paragraph 23 of Article II authorizes the Conference to add a state to Annex 1 by following the procedures set forth in paragraph 22 of Article II for decisions on matters of substance, i.e., consensus, or if consensus is not possible, decision by two-thirds majority of the members present and voting. Pursuant to paragraph 23 of Article II, any other changes to Annex 1, e.g., moving a state from one geographic region to another, requires a consensus decision of the Conference.

The division of states into six geographic regions constitutes a departure from the more common division into five regions that is employed by the UNGA, and that will be employed in the Organization for the Prohibition of Chemical Weapons. CTBT negotiators chose to divide states into six geographic regions primarily because such a structure would parallel the structure of the IAEA.