Gravitational waves (GWs) are the newest tool for exploring the Universe. Advanced Virgo and Advanced LIGO have opened a new window on the Universe by detecting GW signals in the Hz-kHz frequency range. The Pulsar Timing Array experiments have just announced the detection of GWs in the nanohz frequency range.
A new generation of GW interferometric observatories is being prepared to replace the current generation of GW detectors in the next decade. This will make it possible to search almost the entire Universe for GW signals. The Einstein Telescope (ET) is at the forefront of the design, preparation and implementation of a next-generation gravitational wave observatory in Europe. An overview of the scientific objectives, the observatory design, the required technologies and the project organisation is presented.