Dream Theater is an American progressive metal band formed in 1985 under the name Majesty by John Petrucci, John Myung, and Mike Portnoy while they attended Berklee College of Music in Massachusetts, which they consequently dropped out of to further concentrate on the band which would ultimately become Dream Theater. Though a number of lineup changes followed, the three original members remained together along with James LaBrie and Jordan Rudess until September 8, 2010 when Portnoy left the band.

The band is well known for the technical proficiency of its instrumentalists, who have won many awards from music instruction magazines. Guitarist John Petrucci has been named as the third player on the G3 tour six times, more than any invited players. In 2009 he was named the No. 2 best metal guitarist by Joel McIver in his book The 100 Greatest Metal Guitarists. He was also named as one of the "Top 10 Greatest Guitar Shredders of All Time" by GuitarOne magazine. Former drummer Mike Portnoy has won 23 awards from Modern Drummer Magazine and is also the second youngest person (at the age of 37) to be inducted into the Rock Drummer Hall of Fame. John Myung was voted the greatest bassist of all time in a poll conducted by MusicRadar in August through September 2010. The band was inducted into the Long Island Music Hall of Fame in 2010.

The band's highest selling album is the gold selling Images and Words (1992), which reached #61 on the Billboard 200 charts. Both the 1994 release Awake and their 2002 release Six Degrees of Inner Turbulence also entered the charts at #32 and #46 respectively and received mostly positive reviews. Six Degrees of Inner Turbulence also led to Dream Theater becoming the initial band reviewed in the Music Section of Entertainment Weekly during its opening week of release, despite the magazine generally preferring more mainstream music. In 2007, Systematic Chaos entered U.S. Billboard 200 at #19. Dream Theater has sold over 2.1 million albums in the U.S., and over 10 million records worldwide.

The band's tenth studio album, Black Clouds & Silver Linings, was released on June 23, 2009. It entered the U.S. Billboard 200 at #6 and Eurochart Hot 100 at #1, marking their highest entry on either chart.