There are two bands with this title, a well-known metal band from the East Coast of the US and an obscure (and now defunct) rock band from the Midwestern US.

1. Symphony X is an American progressive/power metal band from New Jersey founded in 1994 by guitarist Michael Romeo.

Their 1997 album The Divine Wings of Tragedy and their 2000 release V: The New Mythology Suite have gained the band considerable attention within the progressive metal community. Musically Symphony X is similar to, although heavier than most other progressive metal bands to which they are commonly compared: Dream Theater, Fates Warning and Pain of Salvation. They play in a very syncopated, progressive fashion, also incorporating elements of symphonic metal into their sound. Their music contains strong neoclassical elements in line with the music of Yngwie Malmsteen, Randy Rhoads and other influential neoclassical metal artists.

To date, the band has recorded 9 studio albums and also released one live album Live on the Edge of Forever. Symphony X's latest album was released July 2015, titled Underworld.

Current lineup:
* Michael Romeo (Guitar)
* Russell Allen (Vocals)
* Michael Pinnella (Keyboards)
* Jason Rullo (Drums)
* Michael LePond (Bass)

Former members:
* Rod Tyler (Vocals)
* Thomas Miller (Bass)
* Thomas Walling (Drums) (replaced Jason Rullo temporarily, since Rullo had to take off time for personal issues)

Discography:
* Symphony X [1994]
* The Damnation Game [1995]
* The Divine Wings of Tragedy [1997]
* Twilight in Olympus [1998]
* V: The New Mythology Suite [2000]
* Live on the Edge of Forever [2001]
* The Odyssey [2002]
* Paradise Lost [2007]
* Iconoclast [2011]
* Underworld [2015]

2. Symphony X is a Progressive psychedelic rock band from Wisconsin. Steve Peplin, the vocalist and lead guitarist, has since focused on jazz and is a Prof. of Music @ Milwaukee Tech and founder of Aeclectica Records. They only released one album, entitled Avon Messiah, in 1993.