Abstract: The International Monitoring System (IMS) for the compliance of the Comprehensive Test Ban Treaty is composed of seismic, hydroacoustic, infrasound and radionuclide detection, an international data center, and on-site inspection. It is an international 'big science' operation and relies heavily on physics and physics-based technology. A brief introduction is presented of the main techniques and physical problems related to IMS, its recent developments, and its potential for application to science and sustainability.