The Mid-Season Invitational (MSI) is an annual League of Legends tournament hosted by Riot Games since 2015. It is the second most important international League of Legends tournament aside from the World Championship.

In 2015 and 2016, the event featured the Spring Split champions of the five major competitive League of Legends regional leagues (LEC, LCS, LCK, LMS, LPL), as well as a wildcard team from a less region determined by the International Wildcard Invitational, held a few weeks beforehand. In its inaugural tournament, Chinese team Edward Gaming emerged victorious by defeating South Korean team SK Telecom T1 3–2 in the final.

Since 2017, Spring Split champions from all regions have been participating in the event. The International Wildcard Invitational was replaced by the Play-in Stage. The best Wildcard region receives a direct spot in the World Championship's Group Stage for that year for their Summer Split champion. The top four regions gets the pool 1 spot in the World Championship's Group Stage.

Royal Never Give Up from China and T1 from South Korea are the most successful teams with two MSI titles each.