Seattle Slew (February 15, 1974 – May 7, 2002) was an American thoroughbred race horse that won the Triple Crown of Thoroughbred Racing in 1977, only the tenth horse to accomplish the feat. He was one of very few horses to win the Kentucky Derby with an undefeated record.

He was foaled at Ben Castleman's White Horse Acres Farm near Lexington, Kentucky, by Bold Reasoning out of My Charmer. He was not expected to be a great racehorse. His name came from the city of Seattle, where his owners, Karen and Mickey Taylor of White Swan, Washington were from, and the word slough. Karen felt that the spelling of the word slough, which is a slow-moving channel the loggers in the Northwest used to float logs on, would be too hard for people to remember, so the spelling was changed to Slew, which is pronounced the same way in the western United States.

He started his career September 20, 1976 in the Maiden Special Weight six-furlong event, the fifth race at Belmont Park in New York. He was a big, strong, nearly black two-year-old, and he was nearly unknown. His previous impressive trial runs were not accurately reflected in the daily racing form. The morning line odds on him were 10 to 1, and none of the racing form selectors had picked him to win. However, the public knew better, and as the bets were tallied, the odds lengthened, finally settling at 2 to 1. By the time he reached the gate, Seattle Slew was the favorite by 5 to 2. He gave the public a look at his "War Dance," the prancing on tiptoe that typified his pre-race behavior, and won by five lengths.

He earned Horse of the Year honors for 1977 and was elected to the National Museum of Racing and Hall of Fame.

In the Blood-Horse magazine ranking of the top 100 thoroughbred champions of the 20th Century, Seattle Slew was ranked number 9.