The Cassini-Huygens mission, comprising the NASA Saturn Orbiter and the ESA Huygens Probe, arrived at Saturn in late June 2004. The Huygens probe descended under parachute in Titan's atmosphere on 14 January 2005, 3 weeks after separation from the Orbiter. We discuss here the breakthroughs that the Huygens probe, in conjunction with the Cassini spacecraft, brought to Titan science. We review the achievements ESA's Huygens probe put forward and the context in which it operated. The findings include new localized information on several aspects of Titan science: the atmospheric structure and chemical composition; the aerosols distribution and content; the surface morphology and composition at the probe's landing site; the winds, the electrical properties, and the implications on the origin and evolution of the satellite.