Single-A, formerly known as Class A and sometimes as Low-A, is the fourth-highest level of play in Minor League Baseball in the United States, below Triple-A, Double-A, and High-A. There are 30 teams classified at the Single-A level, one for each team in Major League Baseball (MLB), organized into three leagues: the California League, Carolina League, and Florida State League.

Class A Short Season was a level of play in Minor League Baseball in the United States from 1965 through 2020. In the hierarchy of minor league classifications, it was below Triple-A, Double-A, Class A-Advanced, and Class A. Teams in Class A Short Season played about 75 to 80 games per season, compared to the 130- to 140-game seasons of most professional baseball minor leagues.