Treaty on the Prohibition of Nuclear Weapons


  • Opened for Signature: 20 September 2017
  • Duration: Indefinite
  • Depository: UN Secretary-General
  • Number of Signatories: 70
  • Number of Ratifications: 21
  • Entry into Force: 90 Days after ratification by 50 states

Basic Obligations

The Treaty on the Prohibition of Nuclear Weapons prohibits States Parties from developing, testing, producing, manufacturing, acquiring, possessing, or stockpiling nuclear weapons or other nuclear explosive devices. Signatories are barred from transferring or receiving nuclear weapons and other nuclear explosive devices, control over such weapons, or any assistance with activities prohibited under the Treaty. States are also prohibited from using or threatening to use nuclear weapons and other nuclear explosive devices. Lastly, States Parties cannot allow the stationing, installation, or deployment of nuclear weapons and other nuclear explosive devices in their territory. In addition to the Treaty’s prohibitions, States Parties are obligated to provide victim assistance and help with environmental remediation efforts.

Verification and Compliance

The Treaty on the Prohibition of Nuclear Weapons does not contain a verification regime. Each State Party must maintain its existing safeguards agreements with the International Atomic Energy Agency (IAEA). State Parties that have not yet done so must, at a minimum, conclude a comprehensive safeguards agreement (INFCIRC/153)


Any State Party may propose an amendment to the Treaty at any time after its entry into force. The UN Secretary-General shall circulate the proposal to all States Parties for consideration. If a majority of States Parties register their support for the proposal within 90 days of circulation, it will be considered at the next meeting of States Parties or review conference. The amendment may be adopted by a positive vote of two-thirds of States Parties.


Each State Party has the right to withdraw from the Treaty if it decides that extraordinary events related to the subject matter of the Treaty have jeopardized the supreme interests of its country. Withdrawal will take effect twelve months after the receipt of notification of withdrawal by the Depositary. If the withdrawing State Party is involved in an armed conflict, it will remain bound by the obligations of the Treaty until it is no longer involved in the conflict.

Entry into Force

The Treaty will enter into force 90 days after the fiftieth instrument of ratification, acceptance, approval, or accession has been deposited.

Review Conference

The first conference to review the status of the Treaty will convene after a period of five years following its entry into force. Subsequent review conferences will be held every six years.


Efforts to outlaw nuclear weapons date back to the beginning of the atomic age. However, the Treaty on the Prohibition of Nuclear Weapons has its origins in the Humanitarian Initiative, a group of non-nuclear weapons states who have sought to push nuclear disarmament forward by focusing on the severe humanitarian consequences of nuclear war. As the movement gained support among the international community, backers of the Humanitarian Initiative had high hopes that the 2015 Review Conference on the Nonproliferation of Nuclear Weapons (NPT) would achieve substantial progress toward nuclear disarmament.

Although 160 states endorsed the Humanitarian Initiative at the 2015 NPT Review Conference, the conference failed to adopt a consensus final document. Many countries were dissatisfied with this outcome, and sought to shift efforts to advance the disarmament agenda to an open-ended working group (OEWG) on nuclear disarmament within the United Nations General Assembly. For many advocates of nuclear disarmament, the UN General Assembly was a preferable negotiating forum, as it reaches decision by a majority vote of member states rather than consensus.

At the three open-ended working group meetings in Geneva in 2016, participating states discussed strategies for moving the nuclear disarmament agenda forward. Many states, such as Algeria, Brazil, Indonesia, and South Africa, spoke in favor of opening negotiations for a ban treaty. Nuclear-reliant states present opposed this fast-tracked approach to disarmament, speaking in favor of the “building-blocks,” or “progressive,” approach. The proponents of a ban were successful, and at the third session of the OEWG, States voted to adopt the final report recommending the UN General Assembly convene a conference in 2017 to prohibit nuclear weapons. The vote was 68-22, with 13 countries abstaining. All nine states possessing nuclear weapons boycotted the OEWG, and all dissenting votes came from United States allies. The U.S., which did not attend the OEWG sessions, rejected the final report, calling such efforts to ban nuclear weapons “unrealistic.”

On 27 October 2016, The First Committee of the General Assembly adopted resolution A/C.1/71/L.41 to convene negotiations on a nuclear weapons ban in 2017, and the full General Assembly approved the resolution on 23 December 2016. Opening negotiations took place in New York from 27-31 March 2017 and from 15 June – 7 July, 2017.

The Treaty was adopted on 7 July 2017, after two rounds of negotiations at the UN General Assembly. Both rounds were boycotted by all nuclear weapons possessing states, most NATO countries, and many military allies of nuclear weapons states. Proponents of the Treaty have hailed it as an important step in delegitimizing nuclear weapons and reinforcing the norms against their use, while opponents have criticized the Treaty as political grandstanding which could undermine the NPT.



In January, El Salvador and Saint Lucia ratified the treaty to become state parties, and Cambodia signed the treaty.

On 22 February, South Africa ratified the treaty.


In January, Cuba and Mexico ratified the treaty and became state parties.

On 18 January 2018, Russian Foreign Minister Sergey Lavrov addressed the UN Security Council and directly referenced the Treaty on the Prohibition of Nuclear Weapons as having “unbalanced methods that … are not good for achieving this goal [of a nuclear-free world.”

In March, Palestine and Venezuela ratified the treaty to become state parties.

In advance of the 2018 NPT Preparatory Committee meetings, many signatories restated their support for the Treaty on the Prohibition of Nuclear Weapons. New Zealand, which co-sponsored the General Assembly resolution that mandated negotiations on a nuclear ban treaty, reiterated the treaty’s importance in strengthening the NPT’s Article VI obligations. Austria also authored a working paper that stated only the “total elimination” of nuclear weapons can prevent their use and therefore the Treaty on the Prohibition of Nuclear Weapons “complements and strengthens” the NPT.

In its working paper submitted 18 April, the United States avoided reference to the treaty and emphasized instead “creating the conditions for nuclear disarmament.” When discussing the challenges of compliance, however, the statement did reference the prohibition of nuclear weapons. It stated that, “even a clear prohibition of nuclear weapons, coupled with a detailed plan for their elimination and robust verification provisions, may not be enough, unless the international community can reliably face the challenge of compliance enforcement.”

On 16 April, Bolivia signed the treaty.

In May, Palau, Austria, and Vietnam ratified the treaty.

On 7 June, the Dominican Republic signed the treaty.

On 16 July, a journalist from American magazine The Nation was forcibly removed from a press conference for a summit meeting between U.S. President Donald Trump and Russian Federation President Vladimir Putin in Helsinki, Finland. The journalist had displayed a sign reading “Nuclear Weapons Ban Treaty.”

In July, Costa Rica, New Zealand, Nicaragua and Uruguay ratified the treaty to become state parties.

On 3 August, Colombia signed the treaty.

On 15 August, the Federal Council of Switzerland announced that Switzerland would not sign the Treaty at the moment, but the announcement left open the possibility of re-consideration in the future.

In September, Gambia, Samoa, San Marino, and Vanuatu ratified the treaty. Cook Islands acceded to the treaty.

In September, Angola, Antigua and Barbuda, Benin, Brunei, Guinea-Bissau, Myanmar, Saint Lucia, Seychelles, and Timor-Leste signed the treaty.


On 16 February, states attended the organizational meeting for the March 2017 UN conference to negotiate a nuclear weapons ban. Ambassador Elayne Whyte of Costa Rica was elected as president of the conference. States discussed a draft provisional agenda, conference rules of procedure, and the level of participation to be allowed for non-governmental organizations.

From 27-31 March, the first round of UN negotiations on a nuclear ban treaty took place in New York City. Over 120 countries attended negotiations. However, the U.S. led a boycott of all nine nuclear weapons possessing states and most of their allies. Topics of discussion included the treaty’s objectives, preambular paragraphs and core prohibitions, as well as its legal and institutional arrangements. While states generally agreed on the broad inclusions of the ban treaty, some issues remained contentious. States were divided over whether or not the ban treaty needed its own verification protocols in addition to those that exist under the NPT. States disagreed over how to effectively stop nuclear weapons stockpiling and their transit and transshipment. States also diverged on whether or not to include language banning nuclear testing and prohibiting the threat of use of nuclear weapons..

From 2-12 May, the first Preparatory Committee meeting (PrepCom) for the 2020 Nuclear Non-Proliferation Treaty Review Conference was held in Vienna. Several delegations mentioned the ban treaty negotiations in their statements, and the Chair’s factual summary included reference to various States Parties’ views of the proposed treaty. However, observers noted that the proposed ban treaty was the “elephant in the room,” and both proponents and opponents of the ban treaty were hesitant to raise the issue during formal proceedings.

On 22 May, the president of the UN Conference to negotiate a nuclear ban treaty released the Draft Convention on the Prohibition of Nuclear Weapons based on the first round of negotiations. The draft will be subject to revision at the second round of negotiations in June.

On 7 July, the Treaty on the Prohibition of Nuclear Weapons was adopted by the conference, formally closing two rounds of negotiations that ran from 27-31 March and 15 June to 7 July. 122 countries voted in favor of the treaty; The Netherlands was the only country to vote against the treaty and Singapore abstained from the vote. The treaty opens for signature on 20 September at the 72nd session of the UN General Assembly.

Immediately following the vote, the Unites States, the United Kingdom, and France released a joint statement declaring that they "do not intend to sign, ratify or ever become party” to the treaty. They stated that the treaty ignores the current international security environment, is incompatible with nuclear deterrence, and threatens to severely undermine NPT and the global nonproliferation regime.

On August 9, the Secretary-General of the UN announced that the Treaty on the Prohibition of Nuclear Weapons will open for signature to all states on 20 September 2017.

On 20 September, the Treaty on the Prohibition of Nuclear Weapons opened for signature. Fifty states signed the treaty on it opening day, three of which ratified its terms immediately. Major powers including the United States, Britain, and France remained opposed to the treaty and instead pledged commitment to the Non-Proliferation Treaty.

On 6 October, the Norwegian Nobel Committee awarded the 2017 Nobel Peace Prize to the International Campaign to Abolish Nuclear Weapons, citing its importance as a leading civil society actor in the effort to achieve the prohibition of nuclear weapons in international law. The award was seen as a rebuke to nuclear weapons states and their allies who oppose the Treaty on the Prohibition of Nuclear Weapons.


On 22-26 February, the UN hosted the first session of the second OEWG on concrete legal measures towards a nuclear weapons ban in Geneva, Switzerland. The session addressed possible measures to address the risk posed by an accidental, unauthorized, or intentional detonation of nuclear weapons, as well as the humanitarian risk posed by such a nuclear detonation.

On 2-13 May, the UN hosted the second session of the second OEWG on legal measures and norms to take towards a nuclear weapons ban in Geneva, Switzerland. The session addressed possible pathways to a legal ban on nuclear weapons, and therefore disarmament. Furthermore, the session addressed nuclear weapons in the context of the 21st century, the issue of transparency, and the humanitarian impact of nuclear detonation.

On 5-19 August, the UN hosted the third session of the second OEWG to establish a legal ban against nuclear weapons in Geneva, Switzerland. The OEWG published a final report outlining several key factors: the importance of NWS to undertake the actions required as stated in the 2000 NPT Review Conference, the importance of further multilateral negotiations, and the lack of guidance regarding the implementation of Article VI of the NPT. The document further provided different legal mechanisms through which the international community could enforce Article VI of the NPT, including a prohibition of weapons, their use, NWFZs, or a new legal ban on nuclear weapons or their use.

On 13 October, Resolution A/C.1/71/L.41 (L.41) was submitted to the UN General Assembly First Committee. L.41 was originally sponsored by Austria, Brazil, Ireland, Mexico, Nigeria, and South Africa, but counts fifty-seven States as co-sponsors. It was based on recommendations made in the 2016 OEWG report. L.41 does not establish a nuclear ban treaty, but proposes holding negotiations in 2017 on such an instrument.

On 27 October, the UN General Assembly First Committee voted on L.41. States adopted the resolution to hold negotiations on a nuclear ban treaty in 2017. Despite strong opposition on the part of the nuclear-weapon states and their allies, L.41 was adopted with 123 votes in favor, 38 votes against, and 16 abstentions. The resolution set up a UN conference to negotiate a “Legally Binding Instrument to Prohibit Nuclear Weapons” which will take place in March 2017.


On 29 October, the UNGA First Committee voted to hold a second OEWG regarding negotiations on a nuclear weapons ban.

On 7 December, the UNGA adopted Resolution 70/33, establishing a working group to “substantively address concrete effective legal measures, legal provisions and norms that will need to be concluded to attain and maintain a world without nuclear weapons.”


On 13-14 February, the second Conference on the Humanitarian Impact of Nuclear Weapons was held in Nayarit, Mexico. Participants in the conference reiterated their call for the development of new international standards on nuclear weapons, including a legally binding instrument within a specified timeframe.

On 2 April, Ireland submitted a working paper on behalf of NAC at the 2014 Preparatory Committee for the 2015 NPT Review Conference. The paper discussed the implementation of Article VI of the NPT as an “effective measure” to ban nuclear weapons. The paper further mentioned the “need for a clear, legally-binding, multilateral commitment to achieve nuclear disarmament.”

On 8-9 December, Austria hosted the third Conference on the Humanitarian Impact of Nuclear Weapons in 2014. The Conference looked to strengthen the international nonproliferation and disarmament regime and examined the impacts of intentional or accidental nuclear weapons explosions. Forty three states signed the Austrian Pledge, which recognizes the immediate and long-term consequences of nuclear explosions on health, infrastructure, and the environment and looks to fill the “legal gap” on the prohibition of nuclear weapons. As more states signed on, the Austrian Pledge became the Humanitarian Pledge in May 2015. One hundred and twenty seven states have endorsed the Humanitarian Pledge.


On 2-3 March, the International Campaign to Abolish Nuclear Weapons (ICAN) hosted a civil society forum to demonstrate the humanitarian impact of nuclear weapons use and called upon states to outlaw these weapons.

On 4-5 March, 127 governments, UN agencies, international organizations and members of civil society met in Oslo, Norway to discuss the humanitarian consequences of nuclear weapons use. The first Conference on the Humanitarian Impact of Nuclear Weapons concluded that governments and relief agencies would be unable to adequately respond to the detonation of a nuclear weapon.


On 3 December, the UN General Assembly adopted Resolution 67/56, convening an open-ended working group to develop proposals to take forward multilateral nuclear disarmament negotiations.


The Treaty on the Prohibition of Nuclear Weapons bans the use, possession, development, testing, deployment and transfer of nuclear weapons under international law.

This material is produced independently for NTI by the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies at Monterey and does not necessarily reflect the opinions of and has not been independently verified by NTI or its directors, officers, employees, or agents. Copyright 2019.