A walk-off home run is a type of play in baseball that ends the game. It occurs when the home team hits a home run in the bottom of the final inning, generating enough runs to exceed the opponents score. Because the opponent will not have an opportunity to score any more runs, there is no need to finish the inning, and the teams can walk off the field immediately. The winning runs must still round all three bases and be counted at home plate. A walk-off can be recorded in many ways, including a hit, an error, a walk with the bases loaded, a hit by pitch with the bases loaded, a sacrifice fly, an out (with less than two outs in the inning), a wild pitch, a passed ball, and a balk. As long as enough runs are scored to end the game as the result of the play, it is considered a walk-off.

A walk-off grand slam is a variant of the walk-off home run that occurs when a grand slam exceeds the opponents score in the bottom of the final inning and ends the game. Walk-off celebrations typically consist of an entire baseball team leaving the dugout to meet a player at home plate.

The term "walk-off" originated as "walk-off piece," and was coined by Hall of Famer Dennis Eckersley. It was originally intended to describe a pitchers dejected walk off the field after giving up a game-losing home run, but it soon grew into its own phenomenon.