"2112" (pronounced twenty-one twelve) is a side-long title track from Canadian rock band Rush's 1976 album of the same name. The overture and the first section, Temples of Syrinx, were released as a single and have been featured in most of Rush's setlists since. The "sci-fi" sounds in the beginning of the song were created using an ARP Odyssey synthesizer and an Echoplex tape delay. On the "2112 / Moving Pictures" episode of the documentary series Classic Albums, producer Terry Brown states the synth intro is composed of various parts played by Hugh Syme that were put together in a collage. Since 1997, when any parts of the song are performed live, they are transposed down one full step, as heard on every live album and DVD from Different Stages forward. With the combined movements being twenty minutes and thirty-three seconds long, it is the longest song or suite in Rush's library.

This song is described in the liner notes of the album—its interior and back cover—in two ways:

Both serve as the source, except where otherwise noted, of all that follows.

Lyricist/drummer Neil Peart is credited in the liner notes as acknowledging "the genius of Ayn Rand." Many listeners believe that "2112" is based on Ayn Rand's book, Anthem, as Neil Peart explained the influence that the book had on his music, saying in a 1991 "Rockline" interview:

This part musically foreshadows the rest of the song—incorporating movements from "The Temples Of Syrinx", "Presentation", "Oracle: The Dream", and "Soliloquy"—as well as a guitar adaptation of a familiar part of Tchaikovsky's 1812 Overture. Its sole lyric, at the end, "And the meek shall inherit the Earth", is a reference to the Beatitudes of the New Testament and Psalm 37:11.

The meaning of this part is not explained; some listeners regard this part (and this lyric) as signifying the rise of the Solar Federation, an event described on the back cover as follows:

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