Proliferation Security Initiative (PSI)

Mary Beth Nikitin
Analyst in Nonproliferation


The Proliferation Security Initiative (PSI) was formed to increase international cooperation in interdicting shipments of weapons of mass destruction (WMD), their delivery systems, and related materials. The Initiative was announced by President Bush on May 31, 2003. PSI does not create a new legal framework but aims to use existing national authorities and international law to achieve its goals. Initially, 11 nations signed on to the "Statement of Interdiction Principles" that guides PSI cooperation. As of August 2009, 95 countries have committed formally to the PSI principles, although the extent of participation may vary by country. PSI has no secretariat, but an Operational Experts Group (OEG), made up of 20 PSI participants, coordinates activities. 

Although WMD interdiction efforts took place with international cooperation before PSI was formed, supporters argue that PSI training exercises and boarding agreements give a structure and expectation of cooperation that will improve interdiction efforts. Many observers believe that PSI's "strengthened political commitment of like-minded states" to cooperate on interdiction is a successful approach to counter-proliferation policy. But some caution that it may be difficult to measure the initiative's effectiveness, guarantee even participation, or sustain the effort over time in the absence of a formal multilateral framework. Others support expanding membership and improving inter-governmental and U.S. interagency coordination as the best way to improve the program. President Obama in an April 2009 speech said that PSI should be turned into a "durable international institution," but how this would be implemented is not yet clear. This report will be updated as events warrant.


Date of Report: January 8, 2010
Number of Pages: 12
Order Number: RL34327
Price: $29.95

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