Baseball World Series refers to the championship series of MLB (Major League Baseball) in the United States of America and Canada. It is the culmination of the baseballs postseason every October. World Series is played between two teams - the winner of the National League and the winner of the American League. The winner of Baseball World Series is decided in the best-of-seven playoff (except for 4 times in the event's history when the winner was decided in the best-of-nine playoff) and is given the Baseball World Series Trophy, in addition to World Series rings. The have been different formulas of the championships since the 1850s. Since 1903, Baseball World Series has been a yearly event, except of 1904 and 1994. For different reasons these two dates do not have their relevant marks on the list of world baseball series.

The New York Yankees possess the largest number of World Series titles, having won 26 events. There are eight teams, all founded later than 1961, who have never been awarded a World Series title: Houston Astros, the Texas Rangers, San Diego Padres, Milwaukee Brewers, Washington Nationals, Seattle Mariners, Tampa Bay Devil Rays and Colorado Rockies. Only three of those teams have played in the Series: Houston, San Diego, and Milwaukee.

The opening two games of the World Series are played in the ballpark of the team given the advantage of home-field; the following three are in the ballpark of other team, and the last two, if required are back in the ballpark of the first team. This pattern has been followed since 1924, except for World War II, when traveling was restricted. Until 2003, the team that is awarded the advantage of home-field was changed once a year between the National League and the American League. From the 2003 Baseball World Series anâ on, the league winning the all-star game in the mid-season has been given the advantage of home-field.

The winners of the World Series have from time to time played winter demonstration series against the other world leagues' best players.

A continual legend is that the 'World' in 'Baseball World Series' takes place owing to the sponsorship of the NY World newspaper. However, most baseball researchers refute that claim, illustrating a linear sequence from the expression 'World's Championship Series' (describing the 1903 series) to 'World's Series' (a phrase first appeared in the 1880s and which endured for decades) to 'World Series'. Moreover, examination of the NY World for the pertinent years discovered no evidence of the hypothetical sponsorship.

It's worthy of note that baseball competitions between international squads do take place, especially at the Olympic Games and at the world championships. The United States usually sends a team consisting of minor baseball league players to the Olympics, because it takes place at some stage of the regular season in Major League. The United States of America wasn't represented by any team at the 2004 Olympics, as its team did not go through the qualifying stage. The International Baseball Federation has tried to convince MLB to delay season during the Olympics, so that players from MLB could participate for their national teams, and has consented to make the Olympic tournament shorter if MLB concurs to releasing its players.