Major League Baseball (MLB) is the highest level of play in professional baseball. Major League Baseball specifically refers to the organization that operates North American professional baseball's two major leagues, the National League and the American League. A joint organizational structure had been existed between them since 1903.The American League is in operation under the Designated Hitter Rule while the National League is not operated on the same rule.

The American and National leagues were officially disbanded as separate legal entities in 2000. All the rights and functions were consolidated in the commissioner's office. MLB effectively operates as a single league. It constitutes one of the major professional sports leagues of North America.

New York-based MLB Advanced Media is the production/multimedia wing of MLB. It manages oversees MLB.com and all 30 of the individual teams' websites. MLB Advanced Media holds editorial independence from the League itself as per its charter. But it comes under the same ownership group and revenue-sharing plan. MLB Productions is a similarly-structured wing of the league, focusing on video and traditional broadcast media.

The Major League regular season continues from late March or early April to late September or early October. During February and March, players and teams prepare for the season in spring training, primarily in Florida and Arizona. Three rounds of playoffs follow the regular season. Then there is the World Series in late October.

According to official rule of major League Baseball, all players of a team are required to wear matching uniforms. There was no such rule in force in the early days,. Originally, teams were primarily distinguished by the colors of their stockings. The adoption of sock color was popularized after the success of the Cincinnati Red Stockings. It became the explicit identity of the club. The 1876 Chicago White Stockings actually wore caps of different colors. In 1882, the National League assigned stocking colors to the member clubs: red for Boston, white for Chicago, grey for Buffalo, blue for Worcester, gold for Detroit, green for Troy, and so on. The league also assigned jersey and cap colors that year.

Traditionally, teams wore uniforms that were mostly white with trim in team colors when they played at home. They wore uniforms that were mostly gray with trim in team colors when they played away. With the advent of synthetic fabrics, teams began using more color in their uniforms in the early 1970s. The Pittsburgh Pirates began a trend of multiple combinations of differently colored jerseys and trousers and caps (with the options of black, yellow, and white with pin stripes) in the late 1970s.

In an exhibition game, the All-Star game pits players from the NL, headed up by the manager of the previous NL World Series team, against players from the AL. The 2002 contest ended in an 11-inning tie because both teams were out of pitchers. The fans were not happy with the results. The league which won the game received the benefit of home-field advantage for a two-year trial in 2003 and 2004.

Following this format, the 2005 contest was played in Detroit. The Boston Red Sox and Chicago White Sox took some advantage of the rule in 2004 and 2005 respectively, as each team started the Series with two home victories, giving them good momentum for a sweep. However, the rule did not help the Yankees in 2003, as they lost the Series to Florida in 6 games, or the Detroit Tigers in 2006 as they lost to the St. Louis Cardinals in 5 games.

Major League Baseball is in the transition to a new set of television contracts. For the 2007 season and beyond, the league has three current broadcast partners. FOX Sports will remain with MLB through 2013 and broadcast FOX Saturday Baseball throughout the entire season. FOX will also hold rights to the All-Star Game each season. FOX will also alternate League Championship Series broadcasts, broadcasting the American League Championship Series in odd-numbered years and the National League Championship Series in even-numbered years as part of the new contract. FOX will continue to broadcast all games of the World Series.

Major League Baseball has several blackout rules.A local broadcaster has priority to televise games from the team in their market over national broadcasters. For example, TBS shows many Atlanta Braves games nationally and internationally in Canada. Fox Sports Net (FSN) also shows many games in other areas. If the Braves play a team that FSN or another local broadcaster shows, the local station has the rights for their own local market, TBS will be blacked out for the duration of the game for everyone in the zip code of the market of the team playing against the Braves.