  The XENON1T experiment at the Laboratori Nazionali del Gran Sasso (LNGS) is
the first WIMP dark matter detector operating with a liquid xenon target mass
above the ton-scale. Out of its 3.2t liquid xenon inventory, 2.0t constitute
the active target of the dual-phase time projection chamber. The scintillation
and ionization signals from particle interactions are detected with
low-background photomultipliers. This article describes the XENON1T instrument
and its subsystems as well as strategies to achieve an unprecedented low
background level. First results on the detector response and the performance of
the subsystems are also presented.
