Metal Gear 2: Solid Snake is a 1990 action-adventure stealth game developed and published by Konami for the MSX2. It serves as a sequel to the MSX2 version of the original Metal Gear, written and designed by series's creator Hideo Kojima, who conceived the game in response to Snake's Revenge, a separately-produced sequel that was being developed at the time for the NES specifically for the North American and European markets. The MSX2 version of Solid Snake was only released in Japan, although Kojima would later direct another sequel titled Metal Gear Solid, which was released worldwide for the PlayStation in 1998 to critical acclaim. This later led to Solid Snake being re-released alongside the original Metal Gear as additional content in the Subsistence version of Metal Gear Solid 3 for the PlayStation 2 in 2006 with a full English translation and other revisions. The game has since been re-released as additional content for the HD Edition re-release of Metal Gear Solid 3 for the PlayStation 3, Xbox 360 and PlayStation Vita, as well as part of the Master Collection edition of the original Metal Gear Solid for the PlayStation 4, PlayStation 5, Xbox Series X/S, Nintendo Switch and Windows (via Steam).

Set in 1999, a few years after the events of the original game, Solid Snake must infiltrate a heavily defended territory in Central Asia known as Zanzibar Land to rescue a kidnapped scientist and destroy the revised "Metal Gear D". The game significantly evolved the stealth-based game system of its predecessor, and uses a storyline dealing with themes such as the nature of warfare and nuclear proliferation. It is considered by some to be one of the best 8-bit games ever made.

Solid Snake builds upon the stealth-based gameplay system of its predecessor. As in the original Metal Gear, the player's objective is to infiltrate the enemy's stronghold, while avoiding detection from soldiers, cameras, infrared sensors and other surveillance devices. The biggest change in the game was done to the enemy's abilities. Instead of remaining stationed in one screen like in the first game, enemy soldiers can now patrol different screens across a single map. Moreover, guards now have an expanded 45 degrees field of vision instead of just seeing in straight lines, along with the ability to turn their heads left or right to see diagonally. Enemy guards can also detect sounds, being able to hear any noise made by the player (such as a punch to the wall or a gunshot made without a suppressor) and will investigate the source of the sound once it is made. Guards can also hear sounds made by the player when walking on certain surfaces, which means that one has to be careful when navigating certain areas. If the player is discovered by the enemy, then a counter will be displayed on the upper right side of the screen that will go down after the enemy has lost track of the player. When the counter reaches zero, the alert phase will go off and the game will return to normal.

The player is given a variety of new maneuvers and tools to help them remain undetected and complete the game. For example, the player can now kneel and crawl in addition to walking, allowing the player to avoid making noise over certain terrains, pick up land mines, and hide in tight spaces such as under desks or inside air ducts. A radar with a 3x3 grid on the upper right of the screen shows the player's current area in the center grid (as a red dot), with enemy soldiers as white dots, allowing the player to determine what's ahead. However, the radar is disabled when the game enters alert phase. The radar can also be used with the mine detector equipped to determine the locations of enemy mines or launch Stinger missiles onto an airborne target. Many of the weapons and equipment from the first game are brought over along with new items such as robotic mice used to distract enemies, a camouflaged mat and three different types of rations, each with special attributes. Health and carrying capacity are increased each time a boss is defeated.

The transceiver has also been greatly revamped from the first game as well, with conversations now being context-sensitive rather than being simply area-oriented. The transceiver screen now displays the faces of Snake and the radio contact he's currently communicating with. The player can also talk to children living in the fortress to gain new information; the player is penalized with a loss of health if they kill a child. The areas are more varied than in the previous MSX2 game and a number of puzzles must be fulfilled to complete the game, such as luring a carrier pigeon with a specific kind of ration, chasing after a female spy to the ladies' lavatory, and deciphering secret tap codes to gain new frequency numbers.

The MSX2 version requires the use of either a floppy disk drive or a Game Master II utility cartridge to save progress. In the absence of either media, a password can also be written down to reload progress. Later versions of the game removed the password feature in favor of standardized storage media such as memory cards and internal hard disk drives.

Solid Snake is set in a near-future world in which the Cold War continued into the 1990s, with the game's events taking place in 1999 – three years after the events of the original Metal Gear (later retconned to four years in Metal Gear Solid).

Solid Snake, formerly retired FOXHOUND agent and hero of the original Metal Gear returns as the playable character. His new mission is to rescue the kidnapped Czechoslovak biologist Dr. Kio Marv from the forces of Zanzibar Land. He is assisted by a radio support crew consisting of Roy Kyanbel (spelled "Roy Campbell" in later versions), his new commanding officer; McDonnell Miller, a survival coach and drill instructor; George Kesler ("George Kasler" in later versions), a military strategist; and Yozev Norden (renamed Johan Jacobsen in the later revised versions), a wildlife expert. Also assisting him on-site are Horry White ("Holly White" in later versions), a CIA agent posing as a journalist; Natasha Marcova (Gustava Heffner in later versions), an StB agent and Dr. Marv's bodyguard; and Dr. Petrovich Madnar ("Drago Pettrovich Madnar" in later versions), the Metal Gear designer from the first game, who was captured along with Dr. Marv. Also appearing in the game are Big Boss, the renegade former commander of FOXHOUND, and Grey Fox ("Gray Fox" in later versions), who disappeared following the events of the Outer Heaven incident.