Barclay Tagg (born December 30, 1937 in Lancaster, Pennsylvania) is an American Thoroughbred horse trainer. A 1961 graduate of Pennsylvania State University with a degree in Animal Husbandry, he is best known for conditioning Kentucky Derby, Preakness, and Jockey Club Gold Cup winner Funny Cide...and now for the impressive stable he's been able to build after Funny Cide, his "Big Horse" (term for the horse that puts the trainer "on the map"). With horses like Showing Up and Nobiz Like Shobiz, his stable is growing. Barclay trains horses year round: Spring in New York, Winter in Florida. His assistant trainer is Robin Smullen. (Photos of Tagg and Smullen can be found on the Funny Cide article.)

Formerly a steeplechase jockey, Tagg won his first race in 1972 at Old Liberty Park. He has been a journeyman trainer for many years now, and with Funny Cide became the first trainer to win the Kentucky Derby in his first attempt since Cam Gambolati with Spend a Buck in 1985.

Like the famous trainer of Seabiscuit, the silent Tom Smith, Tagg has a long-standing reputation of being conservative and judicious, so when he gets aggressive with a colt, people pay him heed.