Princess Ida; or, Castle Adamant is a three-act operetta by Gilbert and Sullivan. It is the eighth of their fourteen operettas. It premiered at the Savoy Theatre in London, England on 5 January 1884. It had 246 performances, a short run compared with the team's other operettas. After the operetta closed, it was not revived in London until 1919.
Gilbert based Princess Ida on a play he wrote in 1870 called The Princess. This play was based, in turn, on The Princess, a long poem of 1847 by Alfred, Lord Tennyson. Ida is the only Gilbert and Sullivan operetta in three acts. It is their only operetta to be written in blank verse.
Princess Ida was a great success with early audiences, but the critics did not like it. Sullivan told Gilbert three weeks after the opening that he would not write another comic opera, and it appeared their collaboration was over. Princess Ida has its roots in the work of a poet little read today, and its themes are somewhat dated. The operetta is not a modern audience favorite.