The American League of Professional Baseball Clubs, or simply the American League (AL), is one of two leagues that make up Major League Baseball in the United States and Canada. It developed from the Western League, a minor league based in the Great Lakes states, that eventually aspired to major league status. The league is often called the Junior Circuit because it was elevated to Major League status in 1901, 25 years after the formation of the National League (the "Senior Circuit"). The American League champion plays in the World Series against the National League champion after the end of every season. Through the 2008 season, American League teams have won 61 of the 104 World Series played since 1903, with 26 of those coming from the New York Yankees alone. The Tampa Bay Rays are currently the defending American League champions. The New York Yankees have won 39 American League titles, the most in the league's history, followed by the Oakland Athletics (15) and the Boston Red Sox (12).

With the disappearance of the American Association after the 1891 baseball season, the National League expanded to become a twelve-team league. The National League held a monopoly on major league professional baseball for the remainder of the century. In 1894, Bancroft "Ban" Johnson became the president of the minor Western League. In 1896, he formulated the plan that would eventually see the Western League become the American League. Throughout the latter half of the 1890s, the National League considered contracting from twelve teams to eight. Johnson was determined that if this should happen, then he would be set to place new teams into the abandoned cities and thus take on the established league.

In 1900 the NL finally went through with its planned contraction, eliminating its teams in Baltimore, Cleveland, Louisville, and Washington, D.C.. Johnson thus felt the time was right to take on the established league.