The Sibillini Mountains, or Sibylline Mountains (Italian: Monti Sibillini) are one of the major mountain groups in the Italian Peninsula, and part of the Apennines range. Most of the peaks are over ; the highest is Monte Vettore at .
Since 1993 the area has been part of the Parco Nazionale dei Monti Sibillini (Sibillini Mountains National Park).
The present-day landscape morphology, predominantly U-shaped valleys and glacial depressions, is due to the action of glaciers during the Quaternary period.
The small Lago di Pilato within a deep U-shaped valley below Monte Vettore, is home to a crustacean endemic to this location, Chirocephalus marchesonii.
The area contains stands of beech scattered amongst open subalpine grasslands and meadows maintained by the grazing of sheep.