By definition, a perfect game must be both a no-hitter and a shutout. Since the pitcher cannot control whether or not his teammates commit any errors, the pitcher must be backed up by solid fielding to pitch a perfect game. An error that does not allow a baserunner, such as a misplayed foul ball, does not spoil a perfect game. Weather-shortened contests in which a team has no baserunners and games in which a team reaches first base only in extra innings do not qualify as official perfect games under the present definition. The first confirmed use of the term "perfect game" was in 1908; the current official definition of the term was formalized in 1991. Although it is possible for multiple pitchers to combine for a perfect game (as has happened nine times at the major league level for a no-hitter), to date, every major league perfect game has been thrown by a single pitcher.

During Major League Baseball history, there have been only 18 official perfect games by the current definition. In sum, a perfect game occurs once in about every 11,000 major league contests. No pitcher has ever thrown more than one. The perfect game thrown by Don Larsen in game 5 of the 1956 World Series is the only postseason no-hitter in major league history.

The first two major league perfect games, and the only two of the premodern era, were thrown in 1880, five days apart. The first to accomplish the feat was Lee Richmond, a left-handed pitcher for the Worcester Ruby Legs. Richmond played major-league baseball for only six years, finishing with a losing record. The second perfect game was thrown by John Montgomery Ward for the Providence Grays. Ward, who made the transition from excellent pitcher to excellent position player, went on to be inducted into the Baseball Hall of Fame.

During baseball's "modern era", defined by Major League Baseball as beginning in 1900, sixteen more pitchers have thrown perfect games. Most of the modern-era players to have thrown perfect games were accomplished major league pitchers. Five are members of the Baseball Hall of Fame: Cy Young, Addie Joss, Jim Bunning, Sandy Koufax, and Catfish Hunter. A sixth, Randy Johnson, is a five-time Cy Young Award winner considered certain to be voted into the Hall of Fame when eligible. David Cone also has a Cy Young Award to his name and three other perfect-game throwers, Dennis Martínez, Kenny Rogers, and David Wells, each won over 200 major league games. Mark Buerhle has been an All-Star four times in his ten major league seasons through 2009. For a few the perfect game was the highlight of an otherwise unremarkable career. Mike Witt and Tom Browning were solid major league pitchers; each finished in the top ten in Cy Young voting once. Larsen, Charlie Robertson, and Len Barker were journeyman pitchers; each finished his major-league career with a losing record.

The term "perfect game" is at least as old as 1908. I. E. Sanborn's report for the Chicago Tribune about Joss's performance against the White Sox calls it, "an absolutely perfect game, without run, without hit, and without letting an opponent reach first base by hook or crook, on hit, walk, or error, in nine innings." Several sources have claimed (erroneously) that the first recorded usage of the term "perfect game" was by Ernest J. Lanigan in his Baseball Cyclopedia, made in reference to Robertson's 1922 game. The Chicago Tribune came close to the term in describing Richmond's game in 1880: "Richmond was most effectively supported, every position on the home nine being played to perfection." Similarly, in writing up Ward's perfect game, the New York Clipper described the "perfect play" of Providence's defense