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.