Douglas Vernon DeCinces (/dəˈsɪn.seɪ/ də-SIN-say; born August 29, 1950) is an American former professional baseball player. He played in Major League Baseball (MLB) as a third baseman from 1973 to 1987 for the Baltimore Orioles, California Angels and St. Louis Cardinals. He also played for one season in the Nippon Professional Baseball league for the Yakult Swallows in 1988.

In 1982, DeCinces won the Silver Slugger Award, which is awarded annually to the best offensive player at each position, and was a member of the 1983 American League All-Star team. In 2006, he was inducted into the Baltimore Orioles Hall of Fame.

DeCinces played PONY League Baseball and Colt League Baseball in Northridge, California, with fellow major league player Dwight Evans. He attended and played at Monroe High School in Sepulveda, California and Los Angeles Pierce College, and is in Pierce College's Athletic Hall of Fame.

DeCinces came up through the Orioles system, playing for the Asheville Orioles under manager Cal Ripken Sr. DeCinces famously rescued a pre-teen Cal Ripken Jr. during a pre-game incident involving a teenager firing a rifle into the air adjacent to the stadium where the Orioles played, causing panic amongst those on the field. Ripken Jr. (who was the team's bat boy at the time) was taken away to safety by DeCinces when the gunshots began.

He began his major league career at the age of 23 with the Baltimore Orioles late in the 1973 season. When the Orioles' Hall of Fame third baseman, Brooks Robinson, retired at the end of the 1977 season, DeCinces was given the difficult task of replacing the legendary player. Despite initial hostility from some Orioles fans as Robinson's replacement, he endured to play for the Orioles for a total of nine seasons.

On June 22, 1979, DeCinces hit a game-winning home run at Memorial Stadium off Detroit Tigers reliever Dave Tobik. The Orioles were trailing the Tigers 5-3 going into the bottom of the ninth inning. With one out, Ken Singleton hit a solo home run off Tobik to bring the Orioles within one. Eddie Murray reached base on a single, and, with two outs, DeCinces hit a two-run home run to give the Orioles a 6–5 victory. The win has been called "the night Oriole Magic was born." DeCinces said years later that the game and his home run "triggered something" and that "the emotion just multiplied from there," adding that the ensuing atmosphere of excitement was in no small part due to the excited call of the home run by announcers Bill O'Donnell and Charley Eckman on the Orioles' radio network. The Orioles went on to win the American League pennant in 1979.

DeCinces tagged out Dan Ford who was attempting to advance to third base on a force play that ended Game 2 of the 1979 American League Championship Series.

In 1981, DeCinces got into a feud with teammate Jim Palmer after DeCinces missed a line drive hit by Alan Trammell in a game against the Tigers. According to DeCinces, Palmer "was cussing me out and throwing his hands in the air" after the play. "Those balls have to be caught," Palmer told a paper. "Doug is reluctant to get in front of a ball." "I'd like to know where Jim Palmer gets off criticizing others," DeCinces responded. "Ask anybody–they're all sick of it. We're a twenty-four man team–and one prima donna. He thinks it's always someone else's fault." The feud simmered until June, when manager Earl Weaver said, "I see no cause for concern. The third baseman wants the pitcher to do a little better and the pitcher wants the third baseman to do a little better. I hope we can all do better and kiss and make up...The judge gave me custody of both of them." Palmer ultimately blamed Robinson for the dispute: "If Brooks hadn't been the best third-baseman of all time, the rest of the Orioles wouldn't have taken it for granted that any ball hit anywhere within the same county as Brooks would be judged perfectly, fielded perfectly, and thrown perfectly, nailing (perfectly) what seemed like every single opposing batter."