Gjöll (Old Norse Gjǫll) is the river that separates the living from the dead in Norse mythology. It is one of the eleven rivers traditionally associated with the Élivágar, rivers that existed in Ginnungagap at the beginning of the world.
According to Snorri Sturluson's Gylfaginning, Gjöll originates from the wellspring Hvergelmir in Niflheim, flowing through Ginnungagap, and thence into the worlds of existence. Gjöll is the river that flows closest to the gate of the underworld. Within the Norse mythology, the dead must cross the Gjallarbrú, the bridge over Gjöll, to reach Hel. The bridge, which was guarded by Móðguðr, was crossed by Hermóðr during his quest to retrieve Baldr from the land of the dead. 
In Gylfaginning, Gjöll is one of eleven rivers that rise from Hvergelmir. In the following chapter, these are called the Élivágar and are said to have flowed in Ginnungagap in primordial times.
- John Lindow, Norse Mythology: A Guide to Gods, Heroes, Rituals, and Beliefs, Oxford University Press, 2002, p. 142.
- Snorri Sturluson, Edda, tr. and ed. Anthony Faulkes, The Everyman Library, 1987, pp. 9, 10.
- Snorri Sturluson, tr. Faulkes, p. 29.
- Snorri Sturluson, tr. Faulkes, p. 161.