Eye of Sauron

In the book The Lord of the Rings, the Eye of Sauron refers to Sauron's ability learn about and maintain contact with his spies throughout the realm of Middle-earth. It does not refer to Sauron's eye in a physical sense; throughout the entire book Lord of the Rings Sauron is in the form of a very large humanoid.

In Peter Jackson's movies, The Lord of the Rings: The Fellowship of the Ring and The Lord of the Rings: The Two Towers, Jackson envisions Sauron as being a spirit-like being who has lost his ability to take bodily form. Sauron's only physical presence (at least in the first two movies) is as a giant disembodied red eye, seen in the second movie as floating above Barad-Dûr tower. The Eye is referred to as being "all-seeing", although that is meant as a term of fear and not literally; Sauron is not aware of most events that occur in Middle earth.

Pippin had a brief and frightening encounter with the Eye, after gazing into the Palantír of Orthanc.