The 1990s marked the continued growing influence of money on baseball, leading to the 1994 strike, which saw the World Series cancelled for the first time since 1904, as well as criticism in some circles that only the "big-market" teams could afford to compete. This perception was heightened by the success of the New York Yankees in the late 1990s. The powerhouse of the decade might have been the Atlanta Braves, though they won just one World Series - the Braves made the playoffs 8 of 9 possible years.
Introduced to Major League Baseball during this decade were interleague play, which started in 1997, as well as an expanded playoff system, going from 2 playoff teams in each league to 4, used for the first time in the 1995 Postseason. Both moves were decried by traditionalists but have become an accepted part of the baseball scene.
The most popular event of the decade was the home run record chase of 1998, in which Mark McGwire and Sammy Sosa both surpassed Roger Maris's mark of 61 home runs in a season. A few years later, the race would be cast in a darker light by claims of steroid use against both players.
The home run chase was reflective of a decade in which scoring and home runs went up significantly. Part of this was due to the inauguration of a number of new hitter-friendly ballparks, most notably Mile High Stadium and Coors Field, the two homes of the Colorado Rockies, but also to the popularity of off-season weight-lifting regimes by players, and a spread of sabermetric thinking that valued home runs and walks over small ball tactics. In parallel, the stolen base lost considerable favor as a strategy. The decade also saw the universal adoption of the one-inning closer assisted by a team of relief pitchers used in specialized roles; this gradually became the universal model for bullpen usage. As a result, seasons of 40 and 50 saves, once a rarity, became very common, while the number of complete games pitched fell significantly throughout the decade. However, the number of strikeouts rose significantly.
In minor league baseball, one of the big stories was the formation of the independent leagues. These provided outlets for many players who washed out of the minors or majors to continue to play baseball. Several players also were developed by these independent leagues and wound up in the majors. The independent leagues also led to numerous publicity stunts, including the first female pitcher in minor league baseball, Ila Borders. Also in this decade on the female player front, the Colorado Silver Bullets, composed entirely of women players, were formed, then faded away.
In Asia, The Korea Baseball Organization began allowing the use of foreign players late in the decade and Tyrone Woods, Jay Davis and others made an immediate impact. The Taiwan Major League was started as an alternative to the Chinese Professional Baseball League but did not last long. Nippon Pro Baseball continued to lure some high-profile American players like Kevin Mitchell and Mike Greenwell, but they were generally considered to be busts, while less-notable imports such as Roberto Petagine and Bobby Rose had a longer-lasting impact. Julio Franco was among those bouncing from one league to another, his MLB career seemingly in the past, only to resurface in the next decade.
In a major development, star pitcher Hideo Nomo left Japan to sign a contract with the Los Angeles Dodgers in 1995, becoming the first Japanese player in Major League Baseball since Masanori Murakami in the mid-1960s. Nomo was an instant success in Los Angeles, opening the door to dozens of other Japanese players to come to the Major Leagues in the following seasons. Korean Chan Ho Park also made his Major League debut that season, although he would not establish himself until the following year. By the end of the decade, the presence of Asian players on major League rosters had become a routine event.
- 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
- Bill James: "The 1990s", in The New Bill James Historical Baseball Abstract, The Free Press, New York, NY, 2001, pp. 306-315.
- Jon Pessah: The Game: Inside the Secret World of Major League Baseball's Power Brokers, Little, Brown and Company, New York, NY, 2015. ISBN 978-0316185882
- 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 inflated offensive statistics of star hitters in the 1990s in The Hardball Times, part 1.
-  Article examining the inflated offensive statistics of star hitters in the 1990s in The Hardball Times, part 2.
-  Article examining the inflated offensive statistics of star hitters in the 1990s in The Hardball Times, part 3.
-  Article examining the inflated offensive statistics of star hitters in the 1990s in The Hardball Times, part 4.