This issue of CTBTO Spectrum focuses on the legal aspects of building the verification regime. It sets out to examine the essential role played by facility agreements and other legal arrangements in placing the provisional operation and maintenance of the IMS on a secure legal foundation. An interview with Palitha Kohona, Chief of the Treaty Section of the Office of Legal Affairs at the United Nations in New York, a special feature article by Anthony Aust, former Legal Counsellor of the United Kingdom Foreign Office, and the cover story by Peter Hulsroj, PTS Legal Advisor, give further insights into the unique legal status of the Preparatory Commission and its verification regime.