MASCOT is a small asteroid lander launched on December 3rd, 2014, aboard the Japanese Hayabusa2 asteroid sample-return mission towards the 980 m diameter C-type near-Earth asteroid (NEA) 162173 Ryugu. The lander was jointly developed by the German Aerospace Centre (DLR) and the Centre National d'Etudes Spatiales (CNES). It is equipped with a sensor suite consisting of four fully-fledged instruments: a spectrometer (MicrOmega, IAS Paris), a camera (CAM, DLR Berlin), a radiometer (MARA, DLR Berlin) and a magnetometer (MAG, TU Braunschweig) to investigate Ryugu's surface structure, mineralogical composition, physical properties, thermal behavior and magnetic effects. The MASCOT lander has a total weight of only ~10kg and a size of 30 cm x 30 cm x 20 cm, comparable to a shoebox. Next to the 4 science payloads it accommodates all subsystems to guarantee the survival during the four years cold cruise phase and an on-surface operation and data uplink of up to 2 asteroid days. Upon arrival in Summer 2018 at the target, Hayabusa2 will map NEA Ryugu for several months before it will release MASCOT at an altitude of approx. 100m to free fall on the asteroid's surface. Since MASCOT has no attitude control, it will reach the surface and undergo a certain bouncing phase before it will finally come to rest. A mobility system allows the lander to upright into the correct measurement attitude and to relocate across the asteroids surface after the completion of its first science cycle. The system design, science instruments, and operational concept of MASCOT will be presented, with sidenotes on the development of the mission and its integration with Hayabusa2.