Major League Baseball (MLB) is the highest level of play in North American professional baseball, and is the organization that operates the National League and the American League. In 2000, the two leagues were officially disbanded as separate legal entities, and all of their rights and functions were consolidated in the commissioner's office. Since that time, MLB has operated as a single league, and constitutes one of the major professional sports leagues of the United States. It is composed of 30 teams. Opening Day is the day on which professional baseball leagues begin their regular season. For MLB and most of the minor leagues, this day falls during the first week of April. For baseball fans, Opening Day serves as a symbol of rebirth; writer Thomas Boswell once penned a book titled, Why Time Begins On Opening Day. Many feel that the occasion represents a newness or a chance to forget last season, in that the 30 major league clubs and their millions of fans begin with 0-0 records. Being named the Opening Day starter is an honor, which is often given to the player who is expected to lead the pitching staff that season. It is often given to the pitcher who had the best season the year prior, though there are various strategic reasons why a team's best pitcher might not start on Opening Day. National League Eastern Division Atlanta Braves The Atlanta Braves National League franchise originated in Boston, Massachusetts in 1871. The team has played three different cities: Boston (1871–1952), Milwaukee, Wisconsin (1953–1965), and Atlanta, Georgia (1966–present). Miami Marlins The Marlins franchise entered the National League in 1993 as an expansion team, and was known as the Florida Marlins until 2011. New York Mets The successor to two previous National League franchises in New York City (the Giants and the Dodgers), the New York Mets have played in Queens since 1964, when they vacated the Polo Grounds in Manhattan and moved to Shea Stadium. Philadelphia Phillies The National League franchise in Philadelphia was established in 1883 following the dissolution of the Worcester Worcesters. The team adopted the Philadelphia Phillies name in 1884 and has used the moniker, and been located in the city, since that time. Washington Nationals The Washington Nationals franchise was established in Montreal, Quebec in 1969 as an expansion team, originally known as the Montreal Expos. Central Division Chicago Cubs The Chicago Cubs