Metal Gear Solid 2: Sons of Liberty is a video game directed by Hideo Kojima, developed by Konami Computer Entertainment Japan and published by Konami for the PlayStation 2 in 2001. It is the fourth Metal Gear game produced and directed by Kojima and the direct sequel to Metal Gear Solid. Its release was followed by an expanded edition, Metal Gear Solid 2: Substance for Xbox, PlayStation 2 and Microsoft Windows.

The story revolves around the "Big Shell", a massive offshore clean-up facility that has been seized by a group of terrorists that call themselves "Sons of Liberty". They demand a massive ransom in exchange for the life of the President of the United States, and threaten to destroy the facility and create a cataclysmic environmental disaster if their demands are not met. The motives and identities of many of the antagonists and allies change rapidly, as the protagonists discover a world-shaking conspiracy constructed by a powerful organisation known as the Patriots.

The game was well-received, shipping over 7 million copies worldwide and scoring an average Metacritic aggregate score of 96%, making it the third highest-rated game on the PlayStation 2 and the tied sixth highest-rated game of all time. While the gameplay was universally acclaimed, critics were divided on the philosophical nature and execution of the game's storyline, which explores themes such as memes, social engineering, political conspiracies, and artificial intelligence. It has been considered the first example of a post-modern video game, and has been cited as a primary example of artistic expression in video games. The game was controversial due to its complex post-modern narrative and unconventional protagonist. In 2009, Wired ranked it the 13th "Most Influential Game of the Decade."