Metal Gear (Japanese: METAL GEAR(メタルギア), Hepburn: Metaru Gia) is a franchise of action-adventure stealth games created by Hideo Kojima. Developed and published by Konami, the first game, Metal Gear, was released in 1987 for MSX home computers. The player often takes control of a special forces operative, usually Solid Snake, who is assigned the task of finding the titular superweapon, "Metal Gear", a bipedal walking tank with the ability to launch nuclear weapons.

Several sequels have been released for multiple consoles, which have expanded the original game's plot, adding characters opposing and supporting Snake, while several prequels have explored the origins of Metal Gear and recurring characters. The third game in the series, Metal Gear Solid for the PlayStation, marked a transition to 3D graphics and gained the series international fame.

The series is credited for pioneering and popularizing stealth video games and "cinematic video games". Notable traits of the series include cinematic cutscenes, intricate storylines, offbeat and fourth-wall humor, and exploration of cyberpunk, dystopian, political and philosophical themes, as well as references to Hollywood films. Individual installments have been critically acclaimed, as well as receiving several awards. The series has sold 63.3 million units as of the end of June 2025. The franchise has also been adapted into other media, such as comics, novels, and drama CDs. Solid Snake has also gone on to appear in other games, such as the Super Smash Bros. series, Ape Escape 3, LittleBigPlanet, and Fortnite.

Hideo Kojima designed the original Metal Gear, which debuted in Japan and Europe in 1987 for the MSX2 computer platform. A separate team created a heavily modified Nintendo Entertainment System (NES) port of the game that was released in Japan on December 22, 1987, North America in June 1988, and Europe and Australia sometime in 1989. Konami produced an NES sequel, Snake's Revenge, again without Kojima, released in North America and Europe in 1990. One of that game's designers became acquainted with Kojima and asked him to create a "real Metal Gear sequel". In reaction, Kojima began development of Metal Gear 2: Solid Snake, which was released in Japan in 1990 for the MSX2.

Following Metal Gear 2's completion, Kojima worked on other projects before directing his third Metal Gear game, Metal Gear Solid, for the PlayStation. It began development in 1994 and debuted at the 1996 Tokyo Game Show, before being released in 1998. The success of Metal Gear Solid resulted in a series of sequels, prequels, spin-offs, ports, and remakes for Microsoft Windows, the Game Boy Color, PlayStation 2, Xbox, GameCube, PlayStation 3, PlayStation Portable, PlayStation Vita, Xbox 360, Nintendo 3DS, PlayStation 4, and Xbox One. Metal Gear Solid was followed up by the sequel Metal Gear Solid 2: Sons of Liberty released in November 2001 for the PlayStation 2. A remake of the original Metal Gear Solid called Metal Gear Solid: The Twin Snakes was released for the Nintendo GameCube in early 2004. Later that year, the third numbered entry, Metal Gear Solid 3: Snake Eater, was released on the PlayStation 2. This is the first prequel which was set prior to all the previously released Metal Gear games and which acted as an origin to the franchise. These games were followed by a sequel to Snake Eater, Metal Gear Solid: Portable Ops, which was released on the PlayStation Portable in 2006. The series' main storyline was concluded in Metal Gear Solid 4: Guns of the Patriots for the PlayStation 3 in 2008. The game featured a multiplayer spin-off called Metal Gear Online.

In April 2010, another sequel to Snake Eater, Metal Gear Solid: Peace Walker, was released for the PlayStation Portable and was set shortly after the events of Portable Ops. The spin-off game, Metal Gear Rising: Revengeance, was released in 2013 on the PlayStation 3 and Xbox 360, and in Jan 2014 on Steam (PC). The game is set after Guns of the Patriots and stars Raiden, the protagonist of Sons of Liberty who turned into a cyborg ninja.

Expanded re-releases of games in the series were produced as well, such as Integral (Metal Gear Solid), Substance (Metal Gear Solid 2: Sons of Liberty), and Subsistence (Metal Gear Solid 3: Snake Eater). The series' portable installments are usually set outside the main storyline. Metal Gear: Ghost Babel was released for the Game Boy Color, and several games were released for Sony's PlayStation Portable. In a departure from the series' style, Metal Gear Acid and its sequel used turn-based strategy mechanics based on collectible cards.

On May 18, 2009, a teaser site for the following installment in the Metal Gear series was uploaded by Kojima Production. The site initially consisted of a series of countdowns leading to several flashing letters and the images of two characters looking like a middle-aged Big Boss and a cyborg Raiden. An article published in the July 2009 issue of Famitsu PSP + PS3 covers the content of the site and features an interview with Hideo Kojima. The interview, revealing many details, is heavily censored and was published that way as a request by Kojima, who was directing and designing the new game. Famitsu was to publish the full interview in its following issue. The new game was eventually revealed to be Metal Gear Rising: Revengeance, which was announced on June 1, 2009, at E3, during the Microsoft Press Conference.