The International Noble Gas Experiment (INGE) was formed in 1999 as an informal expert's group of developers of radioactive xenon measurement systems for the International Monitoring System for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) (signed in 1997, but which has not entered into force). The group originally consisted of research and development groups from Germany, France, Russia, Sweden, and the United States, as well as personnel from Provisional Technical Secretariat of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization CTBTO.