Isinglass (1890–1911) was a British Thoroughbred racehorse and sire. In a career which lasted from 1892 until 1895 he ran twelve times and won eleven races. He was the best British two-year-old of 1892 and went on to become sixth winner of the English Triple Crown by winning the 2000 Guineas at Newmarket, The Derby and the St. Leger Stakes at Doncaster in the following year. He was undefeated in his last two seasons, setting a world record for prize money and gaining recognition from contemporary experts as one of the best horses seen in England up to that time.

The Triple Crown of Thoroughbred Racing, often shortened to Triple Crown, is a series of horse races for Thoroughbreds, often restricted to three-year-olds. Winning all three of these Thoroughbred horse races is considered the greatest accomplishment in Thoroughbred racing. The term originated in mid-19th-century England and nations where Thoroughbred racing is popular each have their own Triple Crown series.