The League Championship Series (LCS) is the top level of professional League of Legends in the United States, Canada and Northern Latin America. The esports league is run by Riot Games. Each annual season of competition is divided into three splits, which conclude with a double-elimination tournament between the top teams. At the end of each split, the top teams qualify for international tournaments, currently First Stand, the Mid-Season Invitational and the World Championship.

Established in 2013, the league was initially split into two regions: the European League of Legends Championship Series (EU LCS) and the North American League of Legends Championship Series (NA LCS). The NA LCS featured eight teams, which were determined via a promotion and relegation system. In 2015, the league expanded to ten teams. In 2018, the NA LCS shifted to a franchise system with ten permanent teams, which became eight after the 2023 season. Along with the new model, the league rebranded to simply the League of Legends Championship Series, aligning with the EU LCS's change to League of Legends European Championship, creating unique identities for major regions. The franchise era of the LCS has witnessed several team sales and rebranding efforts. The 2020 season introduced format changes and had to adapt to online play due to the COVID-19 pandemic. In 2021, the LCS again rebranded to the League Championship Series. The 2023 season saw controversy with the LCS Players Association (LCSPA) threatening a player walkout over financial support for teams in the North American Challengers League (NACL).

For the 2025 season, the LCS merged with the Campeonato Brasileiro de League of Legends (CBLOL) and Liga Latinoamérica (LLA) to form the League of Legends Championship of The Americas (LTA), with the LCS name being retired in favor of the name "LTA North" for the conference the LCS would become. However, the LCS will return as a standalone league in 2026, retiring the LTA name in return.

With the exception of some touring events, all games of the LCS are played live at the Riot Games Arena in Los Angeles, California. In addition to a small studio audience, all games are streamed live on Twitch and YouTube.

Prior to the formation of the North American League of Legends Championship series, League of Legends had a growing competitive scene, but a professional league was not a central component of Riot Games' initial business strategy. However, in 2011, professional organized league play became a prominent point of emphasis for Riot after the company hosted its inaugural championship tournament at DreamHack.

On August 6, 2012, Riot Games announced the formation of the League of Legends Championship Series (LCS), a professional gaming league designed to provide support to teams from Europe, Asia, and the United States. The inaugural season of the LCS commenced on February 7, 2013, coinciding with the third season of professional play in League of Legends. As such, it was designated as "Season 3". It was split two regional leagues: the European League of Legends Championship Series (EU LCS) and the North American League of Legends Championship Series (NA LCS). Within these leagues, eight teams representing their respective regions engaged in regional competitions. The top teams in each region advanced to the League of Legends World Championship. The league was not profitable throughout its first season. At the end of 2013, Riot announced a Challenger league, later known as the League of Legends Challenger Series (CS). The league was established with the purpose of serving as a platform for developing talent and providing an opportunity for Challenger-level teams to participate in the LCS via a promotion and relegation system.

Heading into the 2015 season, an expansion tournament was held in both Europe and North America that added two teams in each region, giving the LCS a total of 10 teams per region. Additionally, Riot introduced the concept of "Championship points", which teams would earn based on performance across both splits and playoffs in order to qualify for the World Championship. A new sale of sponsorship rule was instated for the 2015 season, prohibiting companies that facilitated sponsorships for LCS teams from also possessing the branding of those LCS teams. Notably, the GoodGame Agency held ownership of both Europe's Alliance and North America's Evil Geniuses while simultaneously managing sponsorships for both teams. Consequently, in compliance with this new regulation, these teams underwent rebranding, adopting the names Elements and Winterfox, respectively. Furthermore, Curse Inc. faced restrictions on sponsoring LCS team Team Curse, leading to a comprehensive merger of the entire esports organization under the banner of Team Liquid. The league's first female player, Maria "Remilia" Creveling, also joined the league in the 2015.

On May 8, 2016, Riot Games took a series of punitive actions against NA LCS teams Team Impulse and Renegades, along with Challenger Series team Team Dragon Knights. These actions effectively banned these teams from participating in any future sanctioned League of Legends contests due to several infractions, including neglecting player payments, mistreatment of players, and withholding information that would have rendered the teams ineligible for competition. In addition to these sanctions, it was found that, during trade requests between Renegades and Team Dragon Knights, both organizations provided misleading information to League officials regarding the independence of the two teams and the status of players and payments. The evidence indicated that some players continued to be compensated and housed by their former teams even after the trade had been completed. As a result of these actions, former Renegades owner Chris Badawi was permanently banned from participating in Riot-sanctioned leagues, and Christopher Mykles was banned from holding any Riot-sanctioned position within a competing organization for one year. The three teams were given until May 18 to sell all rights and legal claims to their LCS/CS berths.