"I want to thank the Arms Control Association … for being such effective advocates for sensible policies to stem the proliferation of weapons of mass destruction, and most importantly, reduce the risk of nuclear war."
– Senator Joe Biden
January 28, 2004
The Proliferation Security Initiative (PSI) At a Glance

Last Reviewed: 
October 2016

Contact: Kelsey Davenport, Director for Nonproliferation Policy, (202) 463-8270 x102

Updated: October 2016

President George W. Bush announced May 31, 2003 that the United States would lead a new effort, the Proliferation Security Initiative (PSI), to interdict shipments of weapons of mass destruction (WMD) and related goods to terrorists and countries of proliferation concern. The initiative's aim would be "to keep the world's most destructive weapons away from our shores and out of the hands of our common enemies," Bush declared.

Participants: Ten countries originally joined with the United States to shape and promote the initiative. These countries are Australia, France, Germany, Italy, Japan, the Netherlands, Poland, Portugal, Spain, and the United Kingdom. In total, 105 countries have publicly committed to the initiative. Membership in PSI only requires a state to endorse the PSI Statement of Interdiction Principles, a non-binding document that lays out the framework for PSI activities. PSI participants have downplayed the concept of membership in the initiative, explaining in a press statement that PSI is "an activity not an organization." U.S. officials have courted China to join the regime, but so far it has kept its distance, citing concerns about the legality of interdictions.

Mission: The initiative aims to stop shipments of biological, chemical, and nuclear weapons, as well as missiles and goods that could be used to deliver or produce such weapons, to terrorists and countries suspected of trying to acquire WMD. Initiative participants intend to carry out cargo interdictions at sea, in the air, or on land. For some countries this is not a new practice but an enshrinement and expansion of current operations. The United States and other countries have long records of intercepting illegal trade and smuggling activities, including illicit weapons transactions.

Still, the initiative is designed to make it more costly and risky for proliferators to acquire the weapons or materials they seek. By doing so, members hope that other countries will be dissuaded from pursuing weapons in the first place or experience significant delays in their acquisition efforts.

PSI is limited to stopping shipments of WMD and dual-use goods-items that have both civilian, peaceful purposes and that can be used to make weapons-to those countries and nonstate actors viewed as threats by PSI participants. Then-Undersecretary of State for Arms Control and International Security John Bolton indicated in November 2003 that participants will not be targeting the trade of countries perceived as U.S. allies or friends, such as India, Israel, and Pakistan-all three of which possess WMD arsenals, including nuclear weapons.

Principles: The 11 original PSI participants released a set of principles September 4, 2003.[2] The principles call on PSI participants, as well as other countries, to not engage in WMD-related trade with countries of proliferation concern and to permit their own vessels and aircraft to be searched if suspected of transporting such goods. The principles further urge that information on suspicious activities be shared quickly to enable possible interdictions and that all vessels "reasonably suspected" of carrying dangerous cargo be inspected when passing through national airports, ports, and other transshipment points.

Legal Authority: The initiative does not create new law, but rather relies on existing international law to conduct interdictions in international waters or airspace. For example, a ship can be stopped in international waters if it is not flying a national flag or properly registered. It cannot be stopped simply because it is suspected of transporting WMD or related goods. PSI is primarily intended to encourage participating countries to take greater advantage of their own existing national laws to intercept threatening trade passing through their territories, where they have jurisdiction to act. In situations where the legal authority to act may be ambiguous, Bolton said participants might go to the UN Security Council for authorization.

Although the initiative does not create new law, PSI participants are encouraged to develop their national laws and help promote international treaties that criminalize WMD related trafficking.  PSI member states also seek to expand their legal authority to interdict shipments by signing bilateral boarding agreements with select countries to secure expedited processes or pre-approval for stopping and searching their ships at sea. The United States has concluded such agreements with Antigua and Barbuda, Bahamas, Belize, Croatia, Cyprus, Liberia, Malta, the Marshall Islands, Mongolia, Panama and St. Vincent and the Grenadines. Liberia and Panama possess the largest fleets of registered ocean-going vessels in the world.

Structure: PSI is an informal arrangement among countries. To date, there is no list of criteria by which interdictions are to be made (except that the cargo is destined for a recipient that might use it to harm the United States or other countries). There is also no secretariat or formal organization that serves as a coordinating body. Instead, participants aim to readily share information among one another as appropriate and to act when necessary to help seize or thwart dangerous trade. One forum for coordination among PSI members is Operational Experts Group (OEG). The OEG consists of delegations from the most active PSI members, which meet periodically to plan exercises, discuss recent interdictions, and share relevant information. There are currently 21 states that participate in the OEG.

Activities and Interdictions: PSI participants have conducted nearly 50 interdiction exercises since the initiative's inception. The exercises, including mock ship boardings, are intended to increase the participants' capabilities to cooperate with one another. They are also intended to put a public face on the initiative and act as a deterrent to potential proliferators.

U.S. officials claim that there have been successful interdictions since the initiative's launch. In a June 2006 speech, then-Undersecretary of State Robert Joseph claimed that between April 2005 and April 2006 the United States had cooperated with other PSI participants on “roughly two dozen” occasions to prevent transfers of concern. Ulrik Federspiel, Denmark’s ambassador to the United States, asserted at a May 2005 event that “the shipment of missiles has fallen significantly in the lifetime of PSI.”

A recent example of a PSI success was the June 2011 interdiction of the M/V Light, a Belizean flagged freighter suspected of carrying ballistic missile technology from North Korea to Myanmar. U.S. naval forces intercepted the vessel, and forced it to return to North Korea. Although the M/V Light was turned back before it was inspected, the United States would have had the legal authority to do so through its ship-boarding agreement with Belize, a PSI member state.

Status: On May 28, 2013, representatives from seventy-two PSI member states held a High Level Political Meeting in Warsaw on the 10th anniversary of the PSI’s formation. Attending states affirmed four joint statements pledging to conduct “more regular and robust” PSI exercises; promote international treaties criminalizing WMD-related trafficking; share expertise and resources to enhance interdiction capabilities; and to expand “the influence of the PSI globally through outreach to new states and the public.” The United States pledged at the 2013 Warsaw meeting to accede to the 2005 Protocol to the Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation. The United States deposited its ratification in August 2015. 

A mid-level meeting took place in Washington, DC in January 2016 that included representatives from 71 countries. Thomas Countryman, U.S. assistant secretary of state for international security and nonproliferation, said that participants discussed topics such as trends in proliferation, tactics that networks use to ship sensitive materials and technologies, and options to control proliferation financing. Countryman also said that countries shared expertise and resources that should contribute to building countries’ ability to carry out interdictions.

Updated by Ian Williams