Fortnite is an online video game and game platform developed by Epic Games and released in 2017. It is available in seven distinct game mode versions that otherwise share the same general gameplay and game engine: Fortnite Battle Royale, a battle royale game in which up to 100 players fight to be the last person standing; Fortnite: Save the World, a cooperative hybrid tower defense-shooter and survival game in which up to four players fight off zombie-like creatures and defend objects with traps and fortifications they can build; Fortnite Creative, in which players are given complete freedom to create worlds and battle arenas; Lego Fortnite, an open world game collection divided between survival game Lego Fortnite Odyssey and social game Lego Fortnite Brick Life; Rocket Racing, a racing game; Fortnite Festival, a rhythm game; and Fortnite Ballistic, a tactical first-person shooter currently in early access. All game modes except Save the World are free-to-play.

Save the World and Battle Royale were released in 2017 as early access titles, while Creative was released on December 6, 2018. While the Save the World and Creative versions have been successful for Epic Games, Fortnite Battle Royale in particular became an overwhelming success and a cultural phenomenon, drawing more than 125 million players in less than a year, earning hundreds of millions of dollars per month. Fortnite as a whole generated $9 billion in gross revenue up until December 2019, and it has been listed among the greatest games of all time.

Save the World is available for macOS, PlayStation 4, Windows, and Xbox One, while Battle Royale and Creative were released for all those platforms as well as Android and iOS devices and Nintendo Switch. The game also launched with the release of the ninth-generation PlayStation 5, Xbox Series X/S and Nintendo Switch 2 consoles. Furthermore, Lego Fortnite, Rocket Racing, Fortnite Festival, and Fortnite Ballistic are available on all platforms.

Fortnite has multiple game modes, using the same engine; each has similar graphics and art assets. Five of these modes are directly created and managed by Epic Games and its subsidiaries:

In addition to these modes, Fortnite offers the sandbox mode, Fortnite Creative. Within this mode, players are given complete freedom to spawn any item from the Battle Royale gamemode on a personal island, and can create games such as battle arenas, race courses, platforming challenges, and more. Furthermore, it also supports Unreal Editor for Fortnite (UEFN), which allows players to edit worlds using Fortnite assets. Creative and UEFN also allows players to create custom Fall Guys and Teenage Mutant Ninja Turtles games which can be accessible within the Fortnite launcher.

All modes except Save the World are free-to-play; Save the World is pay-to-play. The games are monetized through the use of V-Bucks, in-game currency that can be purchased with real-world funds, but also earned through completing missions and other achievements in Save the World. In other modes, V-Bucks can be used to buy cosmetic items such as character models or the game's battle pass, a tiered progression of customization rewards for gaining experience and completing certain objectives during the course of a Battle Royale season. The battle pass originally was aimed to support Fortnite Battle Royale, and with the expansion of game modes in 2023, two addition passes were added, the Festival Pass for Fortnite Festival and Lego Pass for Lego Fortnite, each which required progression in those modes to receive rewards. In November and December 2024, Epic changed these mechanics, allowing both of those passes to be progressed through experience points earned in any Fortnite game mode, as well as renaming the Festival Pass to Music Pass. Similarly, the Fortnite Crew, a monthly subscription that paid for the cost of the main battle pass and additional cosmetics, was expanded during the same time to encompass the Music and Lego passes.

All modes of Fortnite are cross-platform play compatible, requiring users to use an Epic Games account for cross-saving between platforms.

Fortnite began from an internal game jam at Epic Games following the publishing of Gears of War 3 around 2011. Though it was not initially one of the developed titles during the jam, the concept of merging the construction game genre, representing games like Minecraft and Terraria, and shooter games arose, leading to the foundation of Fortnite. Development of Fortnite slowed due to several issues, including switching from the Unreal Engine 3 to Unreal Engine 4, a deeper role-playing game approach to extend the life of the game, and a switch of art style from a dark theme to a more cartoonish style. Further, Epic was looking to get into the games as a service model, and brought in Chinese publisher Tencent to help; Tencent took a large stake in Epic as part of this, leading to the departure of several executives, including Cliff Bleszinski, who had been a key part of Fortnite's development. Fortnite's approach was changed to be Epic's testbed for games as a service, and further slowed the development.