[en] The Nuclear Smuggling International Technical Working Group (ITWG) is an informal association of nuclear forensic practitioners working in partnership with law enforcement, first responder and nuclear regulatory professionals that cooperate to deter the illicit trafficking of nuclear materials. The objective of the ITWG is to advance the science of nuclear forensics and to provide a common approach and effective technical solutions to governments who request assistance. The ITWG was created in 1996 and since that time over 30 nations and organizations have participated in 12 annual meetings and two analytical round robin trials involving plutonium and high enriched uranium. A third analytical round robin as well as several table-top exercises are planned for later in 2007 and 2008. International interest in the ITWG has grown over the past five years as measured by the number of participants at its annual meetings. This growth has spawned the ITWG Nuclear Forensics Laboratories as a companion technical affiliate focusing exclusively on the scientific aspects of nuclear forensics and nuclear smuggling incident response. (author)