The Metal Gear Solid 4 Database is a downloadable application for the PlayStation 3. It takes the form of an encyclopedia, and catalogues every piece of Metal Gear in-game lore from all seven canonical entries in the series: Metal Gear, Metal Gear 2: Solid Snake, Metal Gear Solid, Metal Gear Solid 2: Sons of Liberty, Metal Gear Solid 3: Snake Eater, Metal Gear Solid: Portable Ops, and Metal Gear Solid 4: Guns of the Patriots.
A user can choose how to navigate the database: either alphabetically or by category. In the case of category, the entries in the encyclopedia can be accessed from an alphabetical list, a timeline of the series' in-game universe or a relationship tree (exclusively showing characters and affiliated groups). Articles will contain highlighted word which link to related articles, and the application keeps track of all articles viewed.
The database was released on June 19, 2008 on the PlayStation Store in North America and Japan. It was released on the European store one week later.
The database was the source of much fan controversy when it was first released, as it contained references to several events in the Metal Gear universe (such as confirming that the Snatcher Project was not merely a rumor), and even retconned certain events itself (such as mentioning that Raiden's memories from his time fighting in wars as a child were erased by Solidus Snake).
By default, the database locks all references to Metal Gear Solid 4 to safeguard against spoilers. In order to unlock this hidden information, the player must have a completed MGS4 save file (and player data file, to ensure the save file was not downloaded). Even when fully unlocked it still contains minor gaps and never fully explains everything.
