Donald Eulon Kessinger (born July 17, 1942) is an American former professional baseball player and manager. He played in Major League Baseball as a shortstop from 1964 to 1979, most prominently as a member of the Chicago Cubs, where he was a six-time All-Star and two-time Gold Glove Award winner. He ended his career playing for the St. Louis Cardinals and the Chicago White Sox.

In the late 1960s and early 1970s, Kessinger was considered one of the best shortstops in baseball. For nine consecutive seasons he formed a productive middle-infield partnership with second baseman Glenn Beckert. He is also notable for being the last player-manager in American League history.

A four sport All-State and All-America athlete for the Forrest City High School Mustangs, Kessinger graduated high school in 1960 and went on to the University of Mississippi. During his collegiate years, he earned All-Conference, All-SEC, and All-America honors in both basketball and baseball for the Rebels, and was initiated into the Sigma Nu fraternity. Kessinger also played for the Peoria Pacers, of the Central Illinois Collegiate League (a summer league for collegiate players) in its founding year, 1963. He was signed by the Chicago Cubs as an amateur free agent on June 19, 1964. Kessinger was assigned to play for the Double-A Fort Worth Cats before making his major league debut on September 7, 1964.

He returned to the minor leagues with the Dallas-Fort Worth Spurs for the 1965 season, but was brought back by the Cubs in June of that year and became their starting shortstop. The 1965 season would mark the first of nine consecutive seasons in which Kessinger would work alongside Cubs' second baseman Glenn Beckert. He ended the season hitting for a .201 batting average and led the National League shortstops in errors but, showed some promise by leading the league in range factor.

As the 1966 season got underway, Kessinger continued to struggle with his hitting when, new Cubs manager Leo Durocher encouraged him to become a switch hitter. With the help of coach Pete Reiser, his hitting began to improve, in posting a .304 batting average during the second half of the season. Durocher made Kessinger his lead off hitter, a spot he would hold for many years. He ended the year with a career-high .274 batting average and led the league's shortstops with 474 assists.

Kessinger continued to improve his fielding and in 1968, he was recognized as one of the top shortstops in the league when he was voted to be the starting shortstop for the National League in the 1968 All-Star Game. At the end of the season, he ranked first among the league's shortstops in range factor and, led the entire league in assists. While he also led the league in errors, he attributed this to the fact that he reached more ground balls than the average shortstop.

Kessinger repeated as an All-Star in 1969, in a year which saw the entire Chicago Cubs infield join him on the 1969 All-Star team, with Kessinger and Cubs' third baseman Ron Santo in the starting line-up. In 1969, he set a major league single-season record for shortstops by playing in 54 games without committing an error, breaking the record previously set by Chico Carrasquel in 1951. The Cubs were in first place in the National League Eastern Division for 180 days of the 1969 season, before going 8–17 in their final 25 games, while the New York "Miracle" Mets went 37–11 in their final 48 games to clinch the Eastern Division pennant. Despite the Cubs' late-season collapse, Kessinger scored 109 runs, hit for a .273 batting average with a career-high 181 hits, including 38 doubles; second-most in the league. He led the league's shortstops in putouts, finished second in fielding percentage and once again led the entire National League in assists. He finished in 15th place in balloting for the 1969 National League Most Valuable Player Award and won his first Gold Glove Award. In his book, The Bill James Historical Baseball Abstract, baseball historian Bill James cited manager Durocher's method of using his regular players everyday without any rest days as a factor in the Cubs' collapse. On September 9, 1969, Kessinger was in the batters box at Shea Stadium when a black cat emerged from under the stands. After staring at Kessinger and Santo (in the on-deck circle), it headed toward the Cubs' bench, where Durocher received a raised tail and hiss.

During a July 4 interview in 1969 with then St. Louis Cardinals sportscaster Harry Caray, Cubs pitcher, Ferguson Jenkins, gave a name to Kessinger's trademark play at shortstop—"The Down Pat". Children from throughout WGN-TV's viewing audience widely copied it on playgrounds and in Little League games, and his fellow players typically stood in awe. Carey noted that Kessinger would regularly go to his right, toward left field, spear the ground ball and then, demonstrating a unique agility, reverse while in the air as he whipped the ball toward first base. "Do you think it might be because Don was a great basketball player?" asked Caray. Without hesitation, Jenkins responded, "In the past five games he's made many great plays to his right. Don has this play down pat."