CHEOPS (Characterizing Exoplanets Satellite) is an ESA scientific mission devoted to the characterization of known exoplanets orbiting bright stars, achieved through the precise measurement of exoplanet radii using the technique of transit photometry. CHEOPS was selected in October 2012 as the first Small-class mission (S) within the Agency’s Scientific Programme, with an implementation cycle drastically shorter than for Medium-class (M) and Large-class (L) missions and strict cost-cap to ESA. Following the phase A/B1 study, CHEOPS was adopted for implementation in February 2014 as a partnership between the ESA Science Programme and Switzerland, with a number of other Member States delivering significant contributions to the instrument development and to operations. The CHEOPS payload is a high precision photometer, with an optical Ritchey-Chrétien telescope with 300 mm effective aperture and a large external baffle to minimize straylight. The CHEOPS spacecraft (280 kg mass, 1.5 m size) is based on a flight-proven platform and is now operating in a dawn-dusk Sun Synchronous Orbit at 700 km altitude. CHEOPS completed the Preliminary Design Review at the end of September 2014, passed the Critical Design Review in May 2016 and the Qualification and Acceptance review in February 2019. CHEOPS was launched on a shared Soyuz flight from the European Space Centre of Kourou on 18 December 2019 (VS23), completing the In-Orbit Commissioning in March 2020. The paper describes the CHEOPS launch campaign, the early operations phase and the In-Orbit Commissioning results, including instrument and spacecraft performance.