Artikel XXI

1. Forty-six months after entry into force of this Treaty, and at five-year intervals thereafter, the Depositary shall convene a conference of the States Parties to conduct a review of the operation of this Treaty.
2. The Depositary shall convene an extraordinary conference of the States Parties, if requested to do so by any State Party which considers that exceptional circumstances relating to this Treaty have arisen, in particular, in the event that a State Party has announced its intention to leave its group of States Parties or to join the other group of States Parties, as defined in Article II, paragraph 1, subparagraph (A). In order to enable the other States Parties to prepare for this conference, the request shall include the reason why that State Party deems an extraordinary conference to be necessary. The conference shall consider the circumstances set forth in the request and their effect on the operation of this Treaty. The conference shall open no later than 15 days after receipt of the request and, unless it decides otherwise, shall last no longer than three weeks.
3. The Depositary shall convene a conference of the States Parties to consider an amendment proposed pursuant to Article XX, if requested to do so by three or more States Parties. Such a conference shall open no later than 21 days after receipt of the necessary requests.
4. In the event that a State Party gives notice of its decision to withdraw from this Treaty pursuant to Article XIX, the Depositary shall convene a conference of the States Parties which shall open no later than 21 days after receipt of the notice of withdrawal in order to consider questions relating to the withdrawal from this Treaty.