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 Inside Out 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.