The Human Equation is the sixth album from the progressive rock project Ayreon by Dutch musician Arjen Anthony Lucassen, released on 25 May 2004 via InsideOut Music. As with other Ayreon albums, it features guest appearances from several musicians previously unrelated to the project, including James LaBrie of Dream Theater, Mikael Åkerfeldt of Opeth, Eric Clayton of Saviour Machine, and Devin Townsend, performing music arranged and written by Lucassen.

As with nearly every Ayreon album, it is a concept album with each character being portrayed by one singer. However unlike previous albums, The Human Equation is not a sci-fi story but take place almost entirely in the mind of a character called Me (played by LaBrie) who is in a coma after a car accident, with each song consisting of one day spent in coma. While his Wife (Marcela Bovio) and Best Friend (Lucassen) are at his side in the real world, Me, trapped in his own mind, encounters representations of his own feelings and recall his life from his childhood to his accident.

The album was released in three different editions: a regular edition with two CDs, a Special Edition with two CDs and a DVD, and a Limited Deluxe Edition with two CDs, a DVD and a 36-page booklet. The album peaked at #7 at Dutch Albums Chart and at #50 at Germany Albums Top 50. The album was also released on vinyl in December 2012.

The Human Equation is one of the few Ayreon albums in which Lucassen did not write all the lyrics (the others are Into the Electric Castle and The Theory of Everything): Townsend wrote all lyrics for his character Rage, while Heather Findlay of Mostly Autumn and Devon Graves of Deadsoul Tribe also wrote some of the lyrics for their characters, Love and Agony. The albums marks the first collaboration between Lucassen and Bovio, selected by Lucassen via an internet female singing contest to play Wife. The following year, Bovio and Lucassen created together progressive/symphonic metal band Stream of Passion.

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