Kojima's choice of composer for Metal Gear Solid 2 was highly publicized in the run-up to the game's release, with him deciding upon Harry Gregson-Williams, a film composer from Hans Zimmer's studio, after watching The Replacement Killers with sound director Kazuki Muraoka. A mix CD containing 18 tracks of Gregson-Williams' work was sent to his office. Flattered by the research put into creating the CD (as some of the tracks were unreleased, and that what tracks he'd worked on for some films were undocumented), he joined the project soon after.
To bypass the language barrier and allow the score to be developed before the cutscenes were finalized, Gregson-Williams was sent short phrases or descriptions of the intended action. The resultant themes then shaped the action sequences in return. Gregson-Williams also arranged and re-orchestrated the original "Metal Gear Solid Main Theme" for use in the game's opening title sequence.
Norihiko Hibino, who had worked on previous Konami games such as Metal Gear: Ghost Babel, was responsible for the in-game music. He also worked on the majority of the game's cutscenes, re-orchestrating Gregson-Williams' "Main Theme" remix for use in several sequences.
As with Metal Gear Solid, the cutscene music includes orchestral and choir pieces, while the in-game soundtrack is scored with ambient music. However, the score as a whole incorporates more electronic elements (particularly breakbeat) than its predecessor, to reflect the plot's thematic thrust of a machine-dominated society. Rika Muranaka again provided a vocal ending theme, a jazz track entitled "Can't Say Goodbye to Yesterday," sung by Carla White. The game's music was released via four CDs: Metal Gear Solid 2: Sons of Liberty Original Soundtrack, Metal Gear Solid 2: Sons of Liberty Soundtrack 2: The Other Side, Metal Gear Solid 2: Substance Limited Sorter (Black Edition) and Metal Gear Solid 2: Substance Ultimate Sorter (White Edition).