William Ratcliff (Вилльям Ратклифф or Вильям Ратклиф in Cyrillic; Vill'jam Ratkliff or Vil'jam Ratklif in transliteration) is an opera in three acts, composed by César Cui during 1861–1868; it was premiered on 14 February 1869 (Old Style) at the Mariinsky Theatre in Saint Petersburg under the conductorship of Eduard Nápravník. Although it was revived in Moscow in 1900 under Mikhail Ippolitov-Ivanov, it never became part of the standard operatic repertoire either in Russia or in the West. Nevertheless, this opera has considerable significance in the history of Russian art music, not only for the fact that it was the first opera by a member of The Five to reach the stage, but also for musical features that suggest experimentation and interrelationships among The Five.