Hymettus (), also Hymettos (; Greek: Υμηττός, romanized: Ymittós pronounced [imiˈtos]; Ancient Greek: Ὑμηττός [hymɛːt.tós]), is a mountain range in the Athens area of Attica, East Central Greece. It is also colloquially known as Trellós (crazy) or Trellóvouno (crazy mountain); the latter originates from the French "très long" (very long) in awe of its winding length of 16 km, as used by French travelers during the occupation of Greece by the Ottomans. Hymettus was assigned the status of a protected area in the EU's Natura 2000 ecological network.

