Major League Baseball is the highest baseball league in the United States and Canada. The league is composed of 30 teams, all are from the United States except for one that is in Canada. Major League Baseball was founded 1869.

Major League Baseball originally an organization that consisted of two separate legal entities, the American League and the National League; however, these two leagues joined together as legal entities in 2000. Now there is only one difference between these two leagues, which is the Designated Hitter Rule, which the American League uses but the National League does not. During games between the American League and the National League, the rules are determined by the home team's league rules.

The season begins with spring training, which usually takes place in southern cities. The season usually begins on the first Sunday in April. Nearly half of the games are played by mid-July, when a break is taken for the All-Star game. The season is then completed on the first Sunday in October. Each team plays 162 games in a season, which determines who will play in the post-season. All six divisional winners and two wild card teams are chosen for the post-season. The American League champion and the National League Champion meet in the World Series.

The first team of Major League Baseball was the Cincinnati Red Stockings, which was the first professional baseball team. The National Association of Professional Base Ball Players, a league that existed in the 1870s, was where current franchises Chicago Cubs and Atlanta Braves got their start.

During World War II, many baseball players were sent to the battlefield; however, baseball continued to be played. After World War II, the color barrier was broken in large part by Jackie Robinson, who was a rising Negro league player. Many black fans who would normally follow Negro league games would watch Jackie Robinson instead of their traditional team when his Brooklyn Dodgers came to town.

Major League Baseball expanded rapidly during the 1950s and 60s. Many new teams were added and some old teams were being relocated. After 1977, no new teams were added for 15 years. Four new teams were added in the 1990s including the Florida Marlins, the Colorado Rockies, the Arizona Diamondbacks, and the Tampa Bay Devil Rays.

Steroid use has been a major topic and concern in Major League Baseball over the last few years. The United States Senate was in charge of an investigation regarding steroid in 2006. Several major superstars were alleged to have used steroids. Some of them have admitted their steroid use, such as Alex Rodriquez and Mark McGuire.