The Theater Equation is a live album and DVD/BluRay by Arjen Anthony Lucassen's progressive rock/metal rock opera project Ayreon. The Theater Equation consists of a live performance, with cast, choir and small orchestra, of the 2004 album The Human Equation. It marks the first time an Ayreon album was played live entirely, and the first Ayreon live release, although two live albums by other Lucassen projects had previously featured Ayreon songs: Live on Earth by Star One (2003) and Live in the Real World by Stream of Passion (2006). The Theater Equation consisted of four shows, all played in Rotterdam between September 18 and 20, 2015, with the last performance being the one recorded for the album.

Most of the cast of the original album was featured on the tour, including James LaBrie of Dream Theater (Me), Marcela Bovio of Stream of Passion (Wife), former Mostly Autumn member Heather Findlay (Love), Eric Clayton (Reason), and Irene Jansen (Passion). Despite the announcement that he will not take part of the shows due to his reluctance to play live and that he will only support the project as a support advisor, Lucassen was on stage after stepping out of the Dream Sequencer at the very end of the show, thus performing the part of Forever of the Stars. Some other regular collaborators of Lucassen joined the project, most notably Anneke van Giersbergen replacing Mikael Åkerfeldt as Fear.

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