Sentinel is a person or thing that keeps guard of a place.

There are also places called Sentinel:

• Sentinel Township in North Dakota,
• Sentinel in Oklahoma,
• The two Sentinel Islands, in the Andaman Islands.

Sentinel can also refer to the following:

• Sentinel is a former British engineering firm. They built steam (and latterly diesel) railway locomotives and road goods vehicles. They specialised in steam engines with unusual vertical boilers. One of these locomotives is currently in use on the preserved ex-colliery line, the Chasewater Railway in the Midlands.
• Sentinel is the name of the first track in Mike Oldfield's musical album Tubular Bells II (1992).
• Sentinel is a codename that was used by fictional superhero Alan Scott, the original Green Lantern.
• The Sentinels are a series of mutant-hunting robots in the Marvel Universe.
• In the movie The Matrix and its sequels, Sentinels are robots that hunt down humans that have escaped from the Matrix. The Sentinels are squid-shaped and are capable of flight.
• In computer programming, a sentinel is a special character that signifies the end of a sequence of characters.

There are several works called The Sentinel:

• The Sentinel is a short story by Arthur C. Clarke that formed the basis for 2001: A Space Odyssey; see .
• The Sentinel is the name of the local evening newspaper published in Stoke-on-Trent, England.
• The Sentinel is the name of the local newspaper published in Holland, Michigan.
• The Sentinel was an American television series.
• The Sentinel was a 1977 film.
• The Sentinel was an album by neo-progressive band Pallas.
• The Sentinel was a computer game for several home computers.
• "The Sentinel" is a song by Judas Priest, from the 1984 album Defenders of the Faith.