World of Warcraft (WoW) is a massively multiplayer online role-playing game (MMORPG) released in 2004 by Blizzard Entertainment. It is the fourth released game set in the fantasy Warcraft universe, which was first introduced by Warcraft: Orcs & Humans in 1994. World of Warcraft takes place within the Warcraft world of Azeroth, approximately four years after the events at the conclusion of Blizzard's previous Warcraft release, Warcraft III: The Frozen Throne. Blizzard Entertainment announced World of Warcraft on September 2, 2001. The game was released on November 23, 2004, on the 10th anniversary of the Warcraft franchise.

With a peak of 12 million subscriptions in October 2010 and Blizzard's final report of 5.5 million subscriptions in October 2015, World of Warcraft remains the world's most-subscribed MMORPG, and holds the Guinness World Record for the most popular MMORPG by subscribers. In January 2014, Blizzard announced that more than 100 million accounts had been created over the game's lifetime.

As with other MMORPGs, players control a character avatar within a game world in third- or first-person view, exploring the landscape, fighting various monsters, completing quests, and interacting with non-player characters (NPCs) or other players. Also similar to other MMORPGs, World of Warcraft requires the player to pay for a subscription, either by buying prepaid game cards for a selected amount of playing time or by using a credit or debit card to pay on a regular basis. Players may instead use a trial account that lets the player character reach level 20 for free but has many features locked.

World of Warcraft is set in the same universe as the Warcraft series of real-time strategy games and has a similar art direction. World of Warcraft contains elements from fantasy, steampunk, and science fiction: such as gryphons, dragons, and elves; steam-powered automata; zombies, werewolves, and other horror monsters; as well as time travel, spaceships, and alien worlds.

World of Warcraft takes place in a 3D representation of the Warcraft universe that players can interact with through their characters. The game world initially consisted of the two continents in Azeroth: Kalimdor and the Eastern Kingdoms. Four separate expansions later added to the game's playable area the realms of Outland and Draenor and the continents of Northrend and Pandaria. As a player explores new locations, different routes and means of transportation become available. Players can access "flight masters" in newly discovered locations to fly to previously discovered locations in other parts of the world. Players can also use boats, zeppelins, or portals to move from one continent to another. Although the game world remains relatively similar from day to day, seasonal events reflecting real world events, such as Halloween, Christmas, Children's Week, Easter, and Midsummer have been represented in the game world. Locations also have variable weather including, among other things, rain, snow, and dust storms.

A number of facilities are available for characters while in towns and cities. In each major city, characters can access a bank to deposit items, such as treasure or crafted items. Each character has access to personal bank storage with the option to purchase additional storage space using in-game gold. Additionally, guild banks are available for use by members of a guild with restrictions being set by the guild leader. Auction houses are available for players to buy and sell items to others in a similar way to online auction sites such as eBay. Players can use mailboxes, which can be found in almost every town. Mailboxes are used to collect items won at auction, and to send messages, items, and in-game money to other characters.

Some of the challenges in World of Warcraft require players to group together to complete them. These usually take place in dungeons—also known as "instances"—that a group of characters can enter together. The term "instance" comes from each group or party having a separate copy, or instance, of the dungeon, complete with their own enemies to defeat and their own treasure or rewards. This allows a group to explore areas and complete quests without others interfering. Dungeons are spread over the game world and are designed for characters of varying progression. A typical dungeon will allow up to five characters to enter as part of a group. Some dungeons require more players to group together and form a "raid" of up to forty players to face some of the most difficult challenges. As well as dungeon-based raid challenges, several creatures exist in the normal game environment that are designed for raids to attack.