The Indianapolis 500, formally known as the Indianapolis 500-Mile Race, and commonly called the Indy 500, is an annual automobile race held at Indianapolis Motor Speedway (IMS) in Speedway, Indiana, United States, an enclave suburb of Indianapolis. 

The event is traditionally held over Memorial Day weekend, usually the last weekend of May. 

It is contested as part of the IndyCar Series, the top level of American open-wheel car racing, a formula colloquially known as "Indy car racing". The track itself is nicknamed the "Brickyard", as the racing surface was paved in brick in the fall of 1909. One yard of brick remains exposed at the start/finish line. 

The event, billed as The Greatest Spectacle in Racing, is considered part of the Triple Crown of Motorsport along with the 24 Hours of Le Mans and the Monaco Grand Prix, with which it typically shares a date.

The inaugural race was held in 1911 and was won by Ray Harroun. The event celebrated its 100th anniversary in 2011, and the 100th running was held in 2016. 

The event was put on hiatus twice, from 1917 to 1918 due to World War I and from 1942 to 1945 due to World War II. In two different periods, the race was part of FIA World Championships; between 1925 and 1928, the World Manufacturers' Championship and between 1950 and 1960, the World Drivers' Championship.

The race was originally advertised as the "International 500-Mile Sweepstakes Race" from 1911 to 1916. However, from its inception, the race has been widely known as the Indianapolis 500 or, more simply as "the 500". 

In 1919, the race was referred to as the "Liberty Sweepstakes" following WWI. From 1920 to 1980, the race officially reverted to the "International Sweepstakes" moniker, as printed on the tickets and other paraphernalia, with slight variations over the years.

The most successful drivers are A. J. Foyt, Al Unser Sr., Rick Mears and Hélio Castroneves, each of whom has won the race four times. The active driver with the most victories is Hélio Castroneves. Rick Mears holds the record for most career pole positions with six. 

The most successful car owner is Roger Penske, owner of the Indianapolis Motor Speedway and Team Penske, which has 19 total wins and 18 poles. Penske also has five wins at the IndyCar Grand Prix, held on the combined road course.inning his second Indy 500 race in 1933. After winning his third title in 1936, he requested another glass but instead received a bottle. 

He was captured by a photographer in the act of swigging from the bottle while holding up three fingers to signify the third win. A local dairy company executive recognized the marketing opportunity in the image and, being unaware Meyer was drinking buttermilk, offered a bottle of milk to the winners of future races. Milk has been presented each year since the.

Following WWII, the race was commonly recognized as "The 500", "The 500-Mile Race", "Indianapolis 500-Mile Race", "Indianapolis 500", or the simple form "Indy 500". Usually the ordinal (e.g. "50th") preceded it. Often the race was also advertised on the radio as the "Annual Memorial Day race", or similar variations.

For the 1981 race, the name "65th Indianapolis 500-Mile Race" was officially adopted, with all references as the "International Sweepstakes" dropped. Since 1981, the race has been formally advertised in this fashion, complete with a unique annual logo with the ordinal almost always included. 

Around that same time, in the wake of the 1979 entry controversy, and the formation of CART, the race changed to an invitational event, rather than an Open, rendering the "sweepstakes" description inappropriate.

For nearly a century, the race eschewed any sort of naming rights or title sponsor, a move, though uncommon in the modern sports world, that was well received by fans.