The 2021 LCS season was the ninth season of the League Championship Series (LCS), a professional esports league for the video game League of Legends. The season was preceded a new preseason tournament, the LCS Lock In, which ran from January 15 to 31, 2021. The season was divided into two splits: Spring and Summer. The Spring Split began on February 5 and culminated with the Mid-Season Showdown finals on April 11, 2021. The Summer Split began on June 4 and culminated with the LCS Championship Final on August 1, 2021.

In 2021, the LCS underwent significant changes. The spring split regular season became a six-week double round-robin, while the spring playoffs were renamed the Mid-Season Showdown. The summer split regular season expanded to a nine-week triple round-robin format. The spring and summer regular season records were combined to determine LCS Championship seeding. Additionally, the league rebranded as the League Championship Series and introduced a new logo and mottos.

Cloud9 won the spring split playoffs, qualifying them for the 2021 Mid-Season Invitational. In the LCS Championship playoffs, 100 Thieves, Team Liquid, and Cloud9 claimed the first, second, and third positions, respectively, earning qualifications to the 2021 World Championship.

The format of the LCS underwent significant changes for the 2021 season. The season introduced the "LCS Lock In," a three-week preseason tournament. The regular season expanded to five games a day over three days a week. The spring split regular season was changed to a double round-robin played over six weeks instead of nine, while maintaining the same number of games as the previous season. Additionally, the spring playoffs were rebranded as the Mid-Season Showdown (MSS). The summer split regular season was expanded to a triple round-robin format that took place over nine weeks. Additionally, the spring and summer regular season records were merged to determine the seeding for the LCS Championship at the end of the summer.^[1]

The league also rebranded from the League of Legends Championship Series into the League Championship Series ahead of the 2021 season. A new logo and two new mottos were introduced: Made by many and All for the game.^[2]

The inaugural LCS Lock In took place from January 15 to 31, 2021, as a three-week preseason tournament. The group stage team selection process began with the top-performing teams from the previous year, namely TSM from group A and FlyQuest from group B. These teams each selected squads to be placed in the opposing group. The Lock-In groups followed a round-robin format, where each team played every other team in their group once, with matches being best-of-one. The top four teams from each group advanced to the knockout stage. The quarterfinals in the knockout stage were contested in a best-of-three series, while the semifinals and final used a best-of-five format. The Lock In champion was awarded a prize of US$150,000, along with an additional $50,000 for a charity of their choice. Additionally, they gained the advantage of side selection for Game 5 of the regular season in case of tied head-to-head records.^[3][4]

The Spring Split regular season ran from February 5 to March 14, 2021. The regular season followed a standard double round-robin format, where each team faced every other team twice. The playoffs ran from April 2 to 24, 2021. The top six teams from the Spring Split advanced to the Mid-Season Showdown (MSS), a double-elimination tournament. This format was similar to the 2020 Spring Playoffs, with the fifth and sixth seeds starting in the lower bracket. One change was the requirement for the first seed to face the fourth seed, and side selection favored the team that had most recently dropped from the upper bracket. Additionally, ties were resolved based on seeding. The winner of the MSS was awarded the first LCS title of 2021 and secured a spot at the 2021 Mid-Season Invitational.^[3]

The lower bracket final and grand final of the MSS took place at the Greek Theatre in Los Angeles, California.^[5]

• Most Valuable Player: Blaber, Cloud9^[7]
• Coaching Staff of the Split: Cloud9^[8]

The Summer Split regular season ran from June 4 to August 1, 2021. The Summer Split regular season featured a triple round robin format, spanning nine weeks of play, where each team faced each other three times. The top eight teams with the highest combined regular season records from both spring and summer secured spots in the LCS Championship playoffs. The top two teams started in the upper bracket semifinals, the following four started in the upper bracket quarterfinals, and the remaining two started in the lower bracket. The LCS Championship playoffs, held from August 7 to 29, featured a double-elimination format. The top team from the playoffs was named the LCS champion, and the top three teams from the playoffs qualified for the 2021 League of Legends World Championship.^[3]

Initially, the LCS Championship lower bracket final and grand final were scheduled to be held at the Prudential Center in Newark, New Jersey. However, due to the increasing number of COVID-19 cases in the United States, these matches were relocated to the LCS Arena in Los Angeles, California, where they took place without a live audience.^[9]

• Most Valuable Player: Spica, Team SoloMid^[11]
• Rookie of the Year: Danny, Evil Geniuses^[12]
• Most Improved Player: Fudge, Cloud9^[13]
• Coaching Staff of the Split: Evil Geniuses^[14]

LCS regular season games were played on Fridays, Saturdays, and Sundays, with Fridays beginning at 3 pm PT and Saturdays and Sundays at 1 pm PT.^[3] A Spanish broadcast was produced by the LCS team FlyQuest.^[15]