One Day International (ODI) is a form of cricket, which is played over 50 overs per side between two national cricket teams. The Cricket World Cup is played in this format. One Day International matches are also called "Limited Overs Internationals (LOI)", because they are limited overs cricket matches between national sides, and if the weather interferes they are not always completed in one day. Important one-day matches, international and domestic, often have two days set aside, the second day being a "reserve" day to allow more chance of the game being completed if a result is not possible on the first day (for instance if play is prevented or interrupted by rain).

The international one-day game is a late twentieth-century development. The first ODI was played on 5 January 1971 between Australia and England at the Melbourne Cricket Ground. When the first three days of the third Test were washed out officials decided to abandon the match and, instead, play a one-off one day game consisting of 40 eight-ball overs per side. Australia won the game by 5 wickets.

In the late 1970s, Kerry Packer established the rival World Series Cricket (WSC) competition, and it introduced many of the features of One Day International cricket that are now commonplace, including coloured uniforms, matches played at night under floodlights with a white ball and dark sight screens, and, for television broadcasts, multiple camera angles, effects microphones to capture sounds from the players on the pitch, and on-screen graphics. The first of the matches with coloured uniforms was the WSC Australians in wattle gold versus WSC West Indians in coral pink, played at VFL Park in Melbourne on 17 January 1979. It was credited with making cricket a more professional sport.