A Night at the Opera is the fourth studio album by the British rock band Queen, released on 28 November 1975, by EMI Records in the United Kingdom and Elektra Records in the United States. Produced by Roy Thomas Baker and Queen, it was reportedly the most expensive album ever recorded at the time of its release.

Named after the Marx Brothers' film of the same name, A Night at the Opera was recorded at various studios across a four-month period in 1975. Due to management issues, Queen had received almost none of the money they earned for their previous albums. Subsequently, they ended their contract with Trident Studios and did not use their studios for the album (the sole exception being "God Save the Queen", which had been recorded the previous year). They employed a complex production that extensively used multitrack recording, and the songs incorporated a wide range of styles, such as ballads, music hall, sea shanties, dixieland, hard rock and progressive rock influences. Aside from their usual equipment, Queen also utilised a diverse range of instruments such as a double bass, harp, ukulele and more.

Upon release, A Night at the Opera became Queen's first number-one album in the UK, topping the UK Albums Chart for four non-consecutive weeks. It peaked at number four on the US Billboard Top LPs & Tape chart and became the band's first platinum-certified album in the US. It also produced the band's most successful single in the UK, "Bohemian Rhapsody", which became their first number one song in the country. Despite being twice as long as the average length of singles during the 1970s, the song became immensely popular worldwide.

Contemporary reviews for A Night at the Opera were positive, with praise for its production and the diverse musical themes, and recognition as the album that established Queen as worldwide superstars. At the 19th Grammy Awards, its first single "Bohemian Rhapsody" received Grammy Award nominations for Best Pop Vocal Performance by a Duo, Group or Chorus and Best Arrangement for Voices. It has since been hailed as Queen's best album, and one of the greatest albums of all time. In 2020, Rolling Stone ranked it number 128 on its list of the "500 Greatest Albums of All Time". It was inducted into the Grammy Hall of Fame in 2018.