William Jennings Bryan "Slim" Harriss[a] (December 11, 1897 – September 19, 1963) was an American professional baseball pitcher.

He played in Major League Baseball (MLB) during the 1920s for the Philadelphia Athletics and Boston Red Sox.

[2] A tall, lanky hurler, Harriss entered the majors in 1920 with the Philadelphia Athletics, playing for them six-and-a-half seasons before joining the Boston Red Sox and playing for them for two-and-a-half seasons.

His most productive season came with the 1925 Athletics, when he recorded career-highs with 19 wins, a 3.49 ERA, and 252+2⁄3 innings pitched.

During the 1926 midseason, he was sent by the Athletics along Fred Heimach and Baby Doll Jacobson to the Red Sox in the same transaction that brought Tom Jenkins and Howard Ehmke to Philadelphia.