Under the CWC, any member-state has the right to request the Director-General of the Organization for the Prohibition of Chemical Weapons (OPCW) to launch a "challenge" inspection. Such an inspection may be conducted at any facility, declared or undeclared, on the territory of another member-state that is suspected of violating the prohibitions of the CWC. The Expert Workshop was attended by 28 experts from 8 countries (Canada, France, Germany, the Netherlands, South Africa, Switzerland, the United Kingdom, and the United States). The focus was on practical solutions to problems that might arise in a CWC challenge inspection of a large, complex facility. As a basis for discussion, the moderators prepared a hypothetical scenario that was divided into several parts. Drawing on this scenario, the workshop participants discussed each stage of the challenge inspection process. In addition a member of the British Arms Control and Disarmament Research Unit gave a presentation on lessons learned from trial challenge inspections at British government facilities. A focus of these exercises has been to develop approaches for protecting national security and sensitive intelligence information. A summary of the workshop discussion addresses the national decision to request a challenge inspection; receipt of an inspection request and notification of the Executive Council; inspection team preparation; special session of the Executive Council; arrival of the inspection team at the point of entry; perimeter negotiations, perimeter activities, and pre-inspection activities; inspection activities; inspection team report; and Executive Council review. Workshop participants agreed that more than 5 years after the CWC became active, the first challenge inspection request is long overdue. Appended list of workshop participants and excerpts from the CWC relevant to challenge inspections