The 1971 World Series matched the defending champion Baltimore Orioles against the Pittsburgh Pirates, with the Pirates winning in seven games. Game 4, played in Pittsburgh, was the first-ever World Series game scheduled to be played at night.

The two teams proved to be evenly matched, as the Series went the full seven games, with the Pirates' Steve Blass pitching a complete game four-hitter in winning Game 7, 2–1, against Mike Cuellar and the Orioles.

The Pirates' Roberto Clemente, who turned into a one-man gang in the Series, became the first Latino player to earn World Series MVP honors. Clemente hit safely in all seven games of the Series, duplicating a feat he had performed in 1960.

Bruce Kison, who appeared in two games and finished with 6.1 innings pitched, tied the record set during the 1907 World Series when he hit three batters during a single series.

These two teams would meet again in the fall classic eight years later.

The Pirates won the National League East division by seven games over the St. Louis Cardinals then defeated the San Francisco Giants, three games to one, in the National League Championship Series. The Orioles won the American League East division by twelve games over the Detroit Tigers then defeated the Oakland A's, three games to none, in the American League Championship Series.

The World Series is the annual championship series of Major League Baseball (MLB), played between the American League and National League champions since 1903. The winner of the World Series championship is determined through a best-of-seven playoff and awarded the Commissioner's Trophy. As the series is played in October, Major League Baseball also refers to it as the "Fall Classic". The most recent World Series was won by the St. Louis Cardinals, who defeated the Texas Rangers in 7 games in 2011.

The New York Yankees of the American League have played in 40 World Series and won 27, and the Oakland/Philadelphia Athletics have played in 14 and won 9. In the National League, the St. Louis Cardinals have played in 18 and won 11, while the San Francisco/New York Giants and Los Angeles/Brooklyn Dodgers have both appeared in 18 and won 6.

Until the formation of the American Association in 1882 as a second major league, the National Association of Professional Base Ball Players (1871–75) and then the National League (founded 1876) represented the top level of organized baseball in the United States. All championships went to whoever had the best record at the end of the season, without a postseason series being played. Starting in 1884 and going through 1890, the National League and the American Association faced each other in a series of games at the end of the season to determine an overall champion. These matchups were disorganized in comparison to the modern Series: games played ranged from as few as three in 1884 (Providence defeated New York 3 games to zero), to a high of 15 in 1887 (Detroit beat St. Louis 10 games to 5), and both the 1885 and 1890 Series ended in ties, each team having won three games with one tie game.

Stephen Robert "Steve" Blass (born April 18, 1942) is a former Major League Baseball right-handed pitcher and a current broadcast announcer for the Pittsburgh Pirates.

Blass was born in Canaan, Connecticut. In a 10-year career, Blass posted a 103–76 record with 896 strikeouts and a 3.63 ERA in 1597 innings pitched.

Signed by the Pittsburgh Pirates in 1960, Blass made his major league debut in 1964, joining the team permanently in 1966. He won 18 games in 1968, including a 2.12 ERA with seven shutouts, both career-highs, and in 1969 won 16 with a career-high 147 strikeouts. From 1969 to 1972, Blass won 60 games, with a career-high 19 victories in 1972. In that season, he made the National League All-Star team.

In the 1971 World Series against the Baltimore Orioles, Blass pitched two complete game wins, allowing only seven hits and two runs in 18 innings. He finished second in the voting for World Series MVP behind teammate Roberto Clemente.

Besides his Series performance, Blass is best known for his sudden and inexplicable loss of control after the 1972 season. His ERA climbed to 9.81 in the 1973 season. He walked 84 batters in 88 ²⁄₃ innings, and struck out only 27. Blass suffered through the 1973 season, then spent most of 1974 in the minor leagues. He retired from baseball in March 1975; two months later writer Roger Angell chronicled Blass's travails in an essay in The New Yorker.