This article grew out of a week-long study in August 2002 to assist ongoing efforts inside and outside the government to remedy some vulnerabilities of the international shipping system on which US and a great deal of world prosperity depend. The study's objective was to identify the most important research initiatives and the major policy issues that need to be addressed in order to improve security of imports using shipping containers, particularly against the importation of nuclear materials and weapons, while maintaining an open trading system. To be effective, a system to detect nuclear weapons or special nuclear material before they reach U.S. ports must be international in scope and reach. It must also be economically acceptable both in terms of total cost and with respect to how these costs are allocated; degrade gracefully when subjected to attack; produce actionable intelligence in a timely manner; treat false alarms realistically; be adaptable to a variety of local physical and political conditions; be auditable, secure yet accessible to the needed foreign and domestic security agencies, and have clear lines of oversight and responsibility. Finally, the system should be flexible enough to allow for regular updates as users and operators gain experience and system performance is reviewed. This study identified a sample technical approach that is feasible technically and operationally and involves components already in the early deployment stage. The approach involves container certification; monitoring at ports of embarkation, debarkation, and continuously during shipment and storage; and continuous data fusion. Specific recommendations regarding system characteristics made by the study include rigorous testing during deployment and in the field, international coordination of standards and protocols, careful analysis of the system for compatibility with pertinent governmental policies and business and labor agreements, and early provision for forward-looking research and development.