Mount Parnitha (Greek: Πάρνηθα, pronounced [ˈparniθa], Katharevousa and Ancient Greek: Πάρνης Parnis/Parnes; sometimes Parnetha) is a lightly forested mountain range north of Athens, the highest on the peninsula of Attica, with an elevation of 1,413 m, and a summit known as Karavola (Καραβόλα). Much of the mountain is designated a national park, and is a protected habitat for wildfowl, first created in 1961. The summit is located 18 km north of Acharnes and about 30 km north of the Athens city center. The mountain covers approximately 250 km² of land. Other peaks include Mavrovouni (Μαυροβούνι), Ornio (1,350 m), Area (1,160 m), Avgo or Avgho (1,150 m), and Xerovouni (Ξεροβούνι, meaning "dry mountain": 1,120 m). It also has two shelters Mpafi and Flampouri. The name of the mountain dates back to ancient times, when it was under the ancient demes of Acharnae and Decelea.

Towns surrounding the mountain include Aspropyrgos, Fyli, Acharnes, Varymbombi, Thrakomakedones, Dekeleia, Avlona and Agios Stefanos as well as the settlement of Agios Merkourios. The highway GR-1 (E75) surrounds the northern and eastern part of the mountain along with the Cephissus river, while the Attiki Odos motorway (GR-6) runs to its south. The mountain offers panoramic views of the mountains northeast of Parnitha, Penteli to the east, the Hymettus to the southeast, the Aigaleo to the south and another to the west; from its summit, one can also see the Thriasian Plain, the Saronic Gulf including the islands of Salamina, Aigina and the North, the South Euboean Gulfs and island of Euboea, and most of central and northern Greater Athens. The view during clear days can extend to northern Boeotia and the Peloponnese.

Parnitha mountain has a warm-summer Mediterranean climate (Csb) with frequent snowfalls in winter and pleasant temperatures in summer. The mountain is significantly wetter than areas of east and southern Attica. The mountain was also affected by several major blizzards, including two in 2005 and 2006, stranding cars and closing roads, as well as the cable car.

Forests of Aleppo Pine cover all slopes beneath 1,000 m altitude, and are often threatened by forest fires, such as happened in 2005, 2007, 2021 and 2023. Above 1,000 m it is covered principally in Greek Fir, grasses and shrubbery, and beneath 300 m mainly farmlands and suburban housing to the east. About 1,000 species of plants can be found on the mountain, including crocus and tulips, and the mountain also provides a native habitat to its red deer (Cervus elaphus), which were known in ancient times. After the traumatic fire in 2007 (see below), they are even scarcer. Several large mines lie to the northwest, and the ore from them was shipped to a nearby factory in industrial areas. Further forest fires occurred in the summers of 2021 and 2023 leaving only northern parts of the mountain forest unburned.

Parnitha has several places of archaeological interest. In antiquity, several fortresses had been built on the mountain, for the defense of the peninsula of Attica and more specifically Classical Athens against the Boeotians and others enemies from the north. Today some fortresses are kept in good condition such as the Phyle fortress, at a height of 687 meters in the west of Parnitha. Other notable fortresses are the Panakton, in the area of Dervenochoria and Eleutherae fortress near Mount Cithaeron. Dekeleia was also an important fortress on the site of modern-day former royal palace in Tatoi, and the fort of Limiko was situated deep inside the mountain, just north of its peak.

A notable monument of later periods is the Monastery of Kleiston. It is a Byzantine monastery dated from 13th century. It is mentioned by Pope Innocent IV in 1209 with the name Monastery of Kyras. Southeast of Parnitha, in a dense forest, is Tatoi Palace. It was the palace of the Greek royal family and it was built in 19th century. Today it is abandoned.

Parnitha has also natural monuments. The cave of Panas is on the west slopes of the mountain at a height of 750 meters. It was a worship site in antiquity. Near the cave there is the steep gorge of Gouras and the gorge of Keladonas river. A beautiful site of the mountain is Beletsi Lake, on the east slopes of the mountain, near Afidnes, and it is important place for migratory birds. In general, the national park is known as the "lungs of Athens".

A casino, the Regency Casino Mont Parnes, is located near the top of the mountain and is served by a suspended cable car. Two shelters are also on Parnitha, the most known of which is Mpafi. A series of trails are found around the mountain as well as forest roads, and also on the mountain is Athens' second transmitter, broadcasting radio and television since the mid-1950s, across the range of television channels from ERT, ANT1, Mega, Alter and more, to satellite, including Super Sport, Seven X and Filmnet, and a multitude of radio including ERA Radio, Klik FM, ANT1 Radio, Ciao FM, Rhythmos, Super Sport FM, Top FM and others. The supporting road connection was paved in the mid-20th century.