The 2018 League of Legends World Championship was an esports tournament for the multiplayer online battle arena video game League of Legends. It was the eighth iteration of the League of Legends World Championship, an annual international tournament organized by the game's developer, Riot Games. It was held from October 1 to November 3, 2018, in cities across South Korea. Twenty four teams qualified for the tournament based on their placement in regional circuits such as those in China, South Korea, Europe, and North America, with twelve of those teams having to reach the group stage via a play-in round. The tournament became known for its very surprising results, numerous upsets, and has often been considered the most unpredictable worlds in League of Legends' history. The tournament also became the most watched esports event in history, reaching a peak of over 200 million concurrent viewers during the finals. It surpassed the viewership of the 2017 League of Legends World Championship, as well as the peak viewership of numerous worldwide sporting events including the Super Bowl.

Multiplayer online battle arena (MOBA) is a subgenre of strategy video games in which two teams of players compete against each other on a predefined battlefield. Each player controls a single character with a set of distinctive abilities that improve over the course of a game and which contribute to the team's overall strategy. The typical objective is for each team to destroy their opponents' main structure, located at the opposite corner of the battlefield. In some MOBA games, the objective can be defeating every player on the enemy team. Players are assisted by computer-controlled units that periodically spawn in groups and march forward along set paths toward their enemy's base, which is heavily guarded by defensive structures. This type of multiplayer online video games originated as a subgenre of real-time strategy, though MOBA players usually do not construct buildings or units. Moreover, there are examples of MOBA games that are not considered real-time strategy games, such as Smite (2014), and Paragon. The genre is seen as a fusion of real-time strategy, role-playing and action games.