Winter league baseball is baseball contested in sports leagues during what is generally considered the baseball off-season.
Annually, the highest level of professional baseball competition, Major League Baseball (MLB), begins with spring training and runs through completion of the World Series in the fall. Winter league baseball takes place in the months between the completion of the World Series and the start of the next season's spring training. As this spans winter in the Northern Hemisphere, winter baseball leagues are located in warm-weather areas such as Central America and the Caribbean, or, less commonly, in the Southern Hemisphere such as in Australia. In Australia, Baseball Victoria holds its own winter league between April and September.
Winter baseball provides an opportunity for prospects to build their skills or demonstrate their capabilities, or for established players to refine their skills or stay in shape. Many notable major-league players have played winter league baseball—during the 1954–55 winter season, the outfield of the Santurce Crabbers in Puerto Rico featured both Willie Mays and Roberto Clemente.
Notable professional baseball leagues operating as winter leagues include:
Champions of leagues based in and around the Caribbean meet annually in the Caribbean Series, normally contested in February.