The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kt liquid scintillator detector in a laboratory 700 m underground. An excellent energy resolution and a large fiducial volume offer exciting opportunities for addressing many important topics in neutrino and astro-particle physics. In this paper, the detector design, the physics prospects, and the subsystems of JUNO including the central detector, veto detector, calibration and JUNO-TAO will be introduced.