In baseball, a rainout refers to a game that is canceled or stopped in progress due to rain. Generally, Major League Baseball teams will continue play in light to moderate rain but will suspend play if it is raining heavily or if there is standing water on the field. Games can also be delayed or canceled for other forms of inclement weather, or if the field is found to be unfit for play, and for other unusual causes (such as the spring training game that was canceled due to a swarm of bees), but rain is by far the most common cause for cancellations or stoppages of play.

Before a baseball game commences, unless it is the second game of a doubleheader, the manager of the home team is in charge of deciding whether or not the game should be delayed or canceled due to rain or other inclement weather. Once the home team manager hands his lineup card to the umpire shortly before the game is to begin, the umpire-in-chief has sole discretion to decide if a game should be delayed or canceled. This also applies to the second game of a doubleheader. Umpires are required by rule to wait at least 30 minutes to see if conditions improve; this is referred to as a rain delay and is not counted as part of the length of the game listed in the box score. In practice, umpires are encouraged to see that games are played if at all possible, and will sometimes wait as long as three hours before declaring a rainout.

If a game is rained out before play begins, it is rescheduled for a later date. If a game is called after play begins but before 4 1/2 innings have been completed (if the home team is ahead) or five innings have been completed (if the visitors are ahead or the game is tied), the game is not an official game. The umpire declares "No Game," the game is played in its entirety at a later date, and statistics compiled during the game are not counted. Games that are stopped after they become official games count in the standings (unless the game is tied, in which case it is replayed from the beginning), and statistics compiled during the game are counted.