The 1960s were the decade of expansion in Major League Baseball. In 1960, there were 16 major league teams, eight in each league, the same sixteen franchises that had existed since 1901 (some of them having moved once or twice in the intervening years). By 1969, there were 24 teams, including one located in Canada, the Montreal Expos. The two leagues had been split into eastern and western divisions, and a second tier of playoffs was added in 1969, the League Championship Series. The start of the "expansion era" is considered a major turning point in baseball history. This is due to changes in the game such as the lengthening of the schedule, and a few years later the addition of new postseason rounds, and trends that started a few years earlier, such as the break-up of New York City's stranglehold on the World Series, the appearance of video records of many games and of detailed play-by-play records, the reform of the minor leagues, the changed demographics of ballplayers, etc.
Montreal was not the only new geographical area to be conquered by Major League Baseball. Three years after the National League had done so, the American League put a foothold on the West Coast in 1961 with the expansion Los Angeles Angels, who were joined in 1968 by the Oakland Athletics, relocated from Kansas City. In the expansion of 1969 both leagues added a third West Coast team, the San Diego Padres in the NL, and the short-lived Seattle Pilots in the AL. The Houston Colt .45's (soon renamed the Houston Astros) and Atlanta Braves became the first teams in the deep south, in 1962 and 1966 respectively, while the Minnesota Twins introduced the fashion of naming a team after a state when they moved from Washington, DC to the Minneapolis-St. Paul area for the 1961 season. Two expansion teams, the (new) Washington Senators of 1961 and the Kansas City Royals of 1969 were put in cities that had recently lost their team to a move.
On the playing field, the 1960s are known as the second deadball era, as offensive levels from 1963 to 1968 were the lowest in baseball history since the Deadball era of the 1900s and 1910s. For a pitcher, playing in Dodger Stadium in the mid 1960s was the most favorable context ever, leading to eye-popping numbers by pitchers such as Sandy Koufax, Don Drysdale or even Ron Perranoski. Things became so twisted in 1968, the so-called Year of the Pitcher, that Bob Gibson could post a 1.12 ERA over 300+ innings, while Carl Yastrzemski would win the American League batting title with a .301 average, the lowest ever for a batting champion. After the season, rule changes were made to lower the pitching mound, and to restrict the size of the strike zone in order to give some leverage back to hitters.
The 1960s were a decade of great pennant races and World Series. The 1960 World Series between the underdog Pittsburgh Pirates and the New York Yankees was decided in favor of Pittsburgh by Bill Mazeroski's walk-off home run in the bottom of the 9th inning of Game 7. The 1962 National League race came down to a three-game playoff between the Los Angeles Dodgers and the San Francisco Giants, with the Giants winning and taking the New York Yankees to the seventh game of a World Series whose outcome was in doubt until the last pitch. 1964 saw close races in both leagues, with the Philadelphia Phillies losing out to the St. Louis Cardinals in a phenomenal collapse over the season's last ten days. The ensuing World Series also went to seven games. The 1967 American League saw probably the greatest pennant race in history, with the Incredible Dream Boston Red Sox, propelled by a superhuman performance by Yastrzemski over the stretch drive, prevailing over three other teams in the season's last week-end, and then losing a tightly-fought seven-game World Series to the Cardinals. The Series again went the distance in 1968, while in 1969, the New York Mets shed their image as lovable losers by overtaking the Chicago Cubs and defeating the heavily-favored Baltimore Orioles in the World Series. 1969 also marked the introduction of the League Championship Series, the first time there was another round of postseason play before the World Series.
The 1960s introduced some major changes in the business aspects of the game. The first long-lasting players' union, the Major League Baseball Players Association, formed the previous decade, hired Marvin Miller as its general counsel and began to fight aggressively to improve the players' lot. The profound impact of that development on player salaries and free agency would begin to be felt by the early 1970s. For the time being, the players' main weapon for improving their financial position was the holdout, the most famous being the joint holdout by pitching stars Don Drysdale and Sandy Koufax of the Los Angeles Dodgers at spring training in 1965. The umpires also began to organize in earnest, in part following the decision by the American League to fire two umpires, Al Salerno and Bill Valentine, during the 1968 season. The two would contest the decision - unsuccessfully - before the National Labor Relations Board, which again would lead to significant changes in the next decade. The first amateur draft was held in 1966, ending the need for a bonus rule and the phenomenon of bonus babies. In turn, Major League Baseball would create the Major League Scouting Bureau in 1974 to assist teams in preparing for the drafts. Many of these events occurred during a period of weak leadership in the Commissioner's office, as retired General William Eckert was not up to the task. In December 1968, he was dismissed with two years remaining on his contract and replaced by Wall Street lawyer Bowie Kuhn, who would exert direct and often controversial leadership from the Commissioner's office, eclipsing the two league presidents.
The minor leagues were in crisis in the 1960s. A number of leagues disappeared, including venerable circuits such as the Three-I League and Georgia-Florida League. Some of the most successful minor league cities of previous decades lost their teams (Minneapolis, MN, St. Paul, MN, Houston, TX, Montreal, QC and Havana), often as a result of expansion, and the remaining teams and leagues were financially unstable. Almost all teams were affiliated with the major leagues, reducing opportunities for young players who fell through the cracks of the draft, and only the Quebec-based Provincial League remained as a professional-level circuit outside of Organized Baseball. It too would disappear by the end of the decade.
The loss of Havana as a minor league city was of course not a result of expansion, but of political developments in Cuba. Shortly after taking power in late 1959, the revolutionary government led by Fidel Castro broke relations with the United States. A direct consequence was to stop Cuban players from playing professionally in the USA - although those who were already signed to contracts played out their careers outside the island. This stopped completely the principal source of foreign talent into Major League Baseball. By the end of the decade, the Dominican Republic had begun to pick up some of the slack.
Yet, the most enduring images of the decade are the 1961 race between teammates Roger Maris and Mickey Mantle of the New York Yankees to break Babe Ruth's record of 60 home runs in a season, and the historical ineptitude of the 1962 New York Mets, who seemed to devise a new way to lose each day on their way to a record of 40-120.
|Years||American League||National League||Postseason||Japan|
|1960||1960 AL||1960 NL||1960 WS||1960 in Japan|
|1961||1961 AL||1961 NL||1961 WS||1961 in Japan|
|1962||1962 AL||1962 NL||1962 WS||1962 in Japan|
|1963||1963 AL||1963 NL||1963 WS||1963 in Japan|
|1964||1964 AL||1964 NL||1964 WS||1964 in Japan|
|1965||1965 AL||1965 NL||1965 WS||1965 in Japan|
|1966||1966 AL||1966 NL||1966 WS||1966 in Japan|
|1967||1967 AL||1967 NL||1967 WS||1967 in Japan|
|1968||1968 AL||1968 NL||1968 WS||1968 in Japan|
|1969||1969 AL||1969 NL||1969 Postseason||1969 in Japan|
- John Florio and Ouisie Shapiro: One Nation Under Baseball: How the 1960s Collided with the National Pastime, University of Nebraska Press, Lincoln, NE, 2017. ISBN 978-0-8032-8690-0
- Daniel A. Gilbert: Expanding the Strike Zone: Baseball in the Age of Free Agency, University of Massachusetts Press, Amherst, MA, 2013. ISBN 978-1-55849-997-3
- George Gmelch: Playing with Tigers: A Minor League Chronicle of the Sixties, University of Nebraska Press, Lincoln, NE, 2016. ISBN 978-0-8032-7681-9
- Paul Hensler: The American League in Transition, 1965-1975: How Competition Thrived When the Yankees Didn't, McFarland, Jefferson, NC, 2013. ISBN 978-0-7864-4626-1
- Paul Hensler: The New Boys of Summer: Baseball's Radical Transformation in the Late Sixties, Rowman & Littlefield, Lanham, MD, 2017. ISBN 978-1-5381-0259-6
- Bill James: "The 1960s", in The New Bill James Historical Baseball Abstract, The Free Press, New York, NY, 2001, pp. 249-275.
- Mike Lupica: "Who ruled the '60s: Gibson, Koufax or Marichal?", mlb.com, April 20, 2020. 
- William J. Ryczek: Baseball on the Brink: The Crisis of 1968, McFarland, Jefferson, NC, 2017. [978-1-4766-6848-2]
- Frank Zimniuch: Baseball's New Frontier: A History of Expansion, 1961-1998, University of Nebraska Press, Lincoln, NE, 2013. ISBN 978-0803239944
-  Article examining the depressed offensive statistics of prominent players in the 1960s in The Hardball Times, part 1.
-  Article examining the depressed offensive statistics of prominent players in the 1960s in The Hardball Times, part 2.
-  Article examining the depressed offensive statistics of prominent players in the 1960s in The Hardball Times, part 3.
-  Article examining the depressed offensive statistics of prominent players in the 1960s in The Hardball Times, part 4.
-  Article examining the depressed offensive statistics of prominent players in the 1960s in The Hardball Times, part 5.